The Different Forms of Flowers on Plants of the Same Species Part 26

I did not at first doubt that this species existed under an hermaphrodite and female form; but we shall presently see that some of the bushes which appear to be hermaphrodites never produce fruit, and these are in fact males. The species, therefore, is polygamous in the sense in which I use the term, and trioecious.

The flowers are frequented by many Diptera and some small Hymenoptera for the sake of the nectar secreted by the disc, but I did not see a single bee at work; nevertheless the other insects sufficed to fertilise effectually female bushes growing at a distance of even 30 yards from any polleniferous bush.

The small anthers borne by the short stamens of the female flowers are well formed and dehisce properly, but I could never find in them a single grain of pollen. It is somewhat difficult to compare the length of the pistils in the two forms, as they vary somewhat in this respect and continue to grow after the anthers are mature. The pistils, therefore, in old flowers on a polleniferous plant are often of considerably greater length than in young flowers on a female plant. On this account the pistils from five flowers from so many hermaphrodite or male bushes were compared with those from five female bushes, before the anthers had dehisced and whilst the rudimentary ones were of a pink colour and not at all shrivelled. These two sets of pistils did not differ in length, or if there was any difference those of the polleniferous flowers were rather the longest. In one hermaphrodite plant, which produced during three years very few and poor fruit, the pistil much exceeded in length the stamens bearing perfect and as yet closed anthers; and I never saw such a case on any female plant. It is a surprising fact that the pistil in the male and in the semi-sterile hermaphrodite flowers has not been reduced in length, seeing that it performs very poorly or not at all its proper function. The stigmas in the two forms are exactly alike; and in some of the polleniferous plants which never produced any fruit I found that the surface of the stigma was viscid, so that pollen-grains adhered to it and had exserted their tubes. The ovules are of equal size in the two forms. Therefore the most acute botanist, judging only by structure, would never have suspected that some of the bushes were in function exclusively males.

Thirteen bushes growing near one another in a hedge consisted of eight females quite dest.i.tute of pollen and of five hermaphrodites with well-developed anthers. In the autumn the eight females were well covered with fruit, excepting one, which bore only a moderate number. Of the five hermaphrodites, one bore a dozen or two fruits, and the remaining four bushes several dozen; but their number was as nothing compared with those on the female bushes, for a single branch, between two and three feet in length, from one of the latter, yielded more than any one of the hermaphrodite bushes. The difference in the amount of fruit produced by the two sets of bushes is all the more striking, as from the sketches above given it is obvious that the stigmas of the polleniferous flowers can hardly fail to receive their own pollen; whilst the fertilisation of the female flowers depends on pollen being brought to them by flies and the smaller Hymenoptera, which are far from being such efficient carriers as bees.

I now determined to observe more carefully during successive seasons some bushes growing in another place about a mile distant. As the female bushes were so highly productive, I marked only two of them with the letters A and B, and five polleniferous bushes with the letters C to G. I may premise that the year 1865 was highly favourable for the fruiting of all the bushes, especially for the polleniferous ones, some of which were quite barren except under such favourable conditions. The season of 1864 was unfavourable. In 1863 the female A produced "some fruit;" in 1864 only 9; and in 1865, 97 fruit. The female B in 1863 was "covered with fruit;" in 1864 it bore 28; and in 1865 "innumerable very fine fruits." I may add, that three other female trees growing close by were observed, but only during 1863, and they then bore abundantly. With respect to the polleniferous bushes, the one marked C did not bear a single fruit during the years 1863 and 1864, but during 1865 it produced no less than 92 fruit, which, however, were very poor. I selected one of the finest branches with 15 fruit, and these contained 20 seeds, or on an average 1.33 per fruit. I then took by hazard 15 fruit from an adjoining female bush, and these contained 43 seeds; that is, more than twice as many, or on an average 2.86 per fruit. Many of the fruits from the female bushes included four seeds, and only one had a single seed; whereas not one fruit from the polleniferous bushes contained four seeds. Moreover when the two lots of seeds were compared, it was manifest that those from the female bushes were the larger. The second polleniferous bush, D, bore in 1863 about two dozen fruit,--in 1864 only 3 very poor fruit, each containing a single seed,--and in 1865, 20 equally poor fruit. Lastly, the three polleniferous bushes, E, F, and G, did not produce a single fruit during the three years 1863, 1864, and 1865.

We thus see that the female bushes differ somewhat in their degree of fertility, and the polleniferous ones in the most marked manner. We have a perfect gradation from the female bush, B, which in 1865 was covered with "innumerable fruits,"--through the female A, which produced during the same year 97,--through the polleniferous bush C, which produced this year 92 fruits, these, however, containing a very low average number of seeds of small size,--through the bush D, which produced only 20 poor fruit,--to the three bushes, E, F, and G, which did not this year, or during the two previous years, produce a single fruit. If these latter bushes and the more fertile female ones were to supplant the others, the spindle-tree would be as strictly dioecious in function as any plant in the world. This case appears to me very interesting, as showing how gradually an hermaphrodite plant may be converted into a dioecious one. (7/7. According to Fritz Muller 'Botanische Zeitung' 1870 page 151, a Chamissoa (Amaranthaceae) in Southern Brazil is in nearly the same state as our Euonymus. The ovules are equally developed in the two forms. In the female the pistil is perfect, whilst the anthers are entirely dest.i.tute of pollen. In the polleniferous form, the pistil is short and the stigmas never separate from one another, so that, although their surfaces are covered with fairly well-developed papillae, they cannot be fertilised, these latter plants do not commonly yield any fruit, and are therefore in function males. Nevertheless, on one occasion Fritz Muller found flowers of this kind in which the stigmas had separated, and they produced some fruit.)

Seeing how general it is for organs which are almost or quite functionless to be reduced in size, it is remarkable that the pistils of the polleniferous plants should equal or even exceed in length those of the highly fertile female plants.

This fact formerly led me to suppose that the spindle-tree had once been heterostyled; the hermaphrodite and male plants having been originally long- styled, with the pistils since reduced in length, but with the stamens retaining their former dimensions; whilst the female plant had been originally short- styled, with the pistil in its present state, but with the stamens since greatly reduced and rendered rudimentary. A conversion of this kind is at least possible, although it is the reverse of that which appears actually to have occurred with some Rubiaceous genera and Aegiphila; for with these plants the short-styled form has become the male, and the long-styled the female. It is, however, a more simple view that sufficient time has not elapsed for the reduction of the pistil in the male and hermaphrodite flowers of our Euonymus; though this view does not account for the pistils in the polleniferous flowers being sometimes longer than those in the female flowers.

Fragaria vesca, Virginiana, chiloensis, etc. (ROSACEAE).

A tendency to the separation of the s.e.xes in the cultivated strawberry seems to be much more strongly marked in the United States than in Europe; and this appears to be the result of the direct action of climate on the reproductive organs. In the best account which I have seen, it is stated that many of the varieties in the United States consist of three forms, namely, females, which produce a heavy crop of fruit,--of hermaphrodites, which "seldom produce other than a very scanty crop of inferior and imperfect berries,"--and of males, which produce none. (7/8. Mr. Leonard Wray 'Gardener's Chronicle' 1861 page 716.) The most skilful cultivators plant "seven rows of female plants, then one row of hermaphrodites, and so on throughout the field." The males bear large, the hermaphrodites mid-sized, and the females small flowers. The latter plants produce few runners, whilst the two other forms produce many; consequently, as has been observed both in England and in the United States, the polleniferous forms increase rapidly and tend to supplant the females. We may therefore infer that much more vital force is expended in the production of ovules and fruit than in the production of pollen. Another species, the Hautbois strawberry (F.

elatior), is more strictly dioecious; but Lindley made by selection an hermaphrodite stock. (7/9. For references and further information on this subject, see 'Variation under Domestication' chapter 10 2nd edition volume 1 page 375.)

Rhamnus catharticus (RHAMNEAE).

(FIGURE 7.13. Rhamnus catharticus (from Caspary.) Left: Long-styled male.

Right: Short-styled male.)

(FIGURE 7.14. Rhamnus catharticus.

Left: Long-styled female.

Right: Short-styled female.)

This plant is well known to be dioecious. My son William found the two s.e.xes growing in about equal numbers in the Isle of Wight, and sent me specimens, together with observations on them. Each s.e.x consists of two sub-forms. The two forms of the male differ in their pistils: in some plants it is quite small, without any distinct stigma; in others the pistil is much more developed, with the papillae on the stigmatic surfaces moderately large. The ovules in both kinds of males are in an aborted condition. On my mentioning this case to Professor Caspary, he examined several male plants in the botanic gardens at Konigsberg, where there were no females, and sent me the drawings in Figure 7.13.

In the English plants the petals are not so greatly reduced as represented in this drawing. My son observed that those males which had their pistils moderately well-developed bore slightly larger flowers, and, what is very remarkable, their pollen-grains exceeded by a little in diameter those of the males with greatly reduced pistils. This fact is opposed to the belief that the present species was once heterostyled; for in this case it might have been expected that the shorter-styled plants would have had larger pollen-grains.

In the female plants the stamens are in an extremely rudimentary condition, much more so than the pistils in the males. The pistil varies considerably in length in the female plants, so that they may be divided into two sub-forms according to the length of this organ. Both the petals and sepals are decidedly smaller in the females than in the males; and the sepals do not turn downwards, as do those of the male flowers when mature. All the flowers on the same male or same female bush, though subject to some variability, belong to the same sub-form; and as my son never experienced any difficulty in deciding under which cla.s.s a plant ought to be included, he believes that the two sub-forms of the same s.e.x do not graduate into one another. I can form no satisfactory theory how the four forms of this plant originated.

Rhamnus lanceolatus.

This plant exists in the United States, as I am informed by Professor Asa Gray, under two hermaphrodite forms. In the one, which may be called the short-styled, the flowers are sub-solitary, and include a pistil about two-thirds or only half as long as that in the other form; it has also shorter stigmas. The stamens are of equal length in the two forms; but the anthers of the short-styled contain rather less pollen, as far as I could judge from a few dried flowers. My son compared the pollen-grains from the two forms, and those from the long-styled flowers were to those from the short-styled, on an average from ten measurements, as 10 to 9 in diameter; so that the two hermaphrodite forms of this species resemble in this respect the two male forms of R. catharticus. The long-styled form is not so common as the short-styled. The latter is said by Asa Gray to be the more fruitful of the two, as might have been expected from its appearing to produce less pollen, and from the grains being of smaller size; it is therefore the more highly feminine of the two. The long-styled form produces a greater number of flowers, which are cl.u.s.tered together instead of being sub- solitary; they yield some fruit, but as just stated are less fruitful than the other form, so that this form appears to be the more masculine of the two. On the supposition that we have here an hermaphrodite plant becoming dioecious, there are two points deserving notice; firstly, the greater length of the pistil in the incipient male form; and we have met with a nearly similar case in the male and hermaphrodite forms of Euonymus compared with the females. Secondly, the larger size of the pollen-grains in the more masculine flowers, which perhaps may be attributed to their having retained their normal size; whilst those in the incipient female flowers have been reduced. The long-styled form of R. lanceolatus seems to correspond with the males of R. catharticus which have a longer pistil and larger pollen-grains. Light will perhaps be thrown on the nature of the forms in this genus, as soon as the power of both kinds of pollen on both stigmas is ascertained. Several other species of Rhamnus are said to be dioecious or sub-dioecious. (7/10. Lecoq 'Geogr. Bot.' tome 5 1856 pages 420- 26.) On the other hand, R. frangula is an ordinary hermaphrodite, for my son found a large number of bushes all bearing an equal profusion of fruit.

Epigaea repens (ERICACEAE).

This plant appears to be in nearly the same state as Rhamnus catharticus. It is described by Asa Gray as existing under four forms. (7/11. 'American Journal of Science' July 1876. Also 'The American Naturalist' 1876 page 490.) (1.) With long style, perfect stigma, and short abortive stamens. (2.) Shorter style, but with stigma equally perfect, short abortive stamens. These two female forms amounted to 20 per cent of the specimens received from one locality in Maine; but all the fruiting specimens belonged to the first form. (3.) Style long, as in Number 1, but with stigma imperfect, stamens perfect. (4.) Style shorter than in the last, stigma imperfect, stamens perfect. These two latter forms are evidently males. Therefore, as Asa Gray remarks, "the flowers may be cla.s.sified into two kinds, each with two modifications; the two main kinds characterised by the nature and perfection of the stigma, along with more or less abortion of the stamens; their modifications, by the length of the style." Mr. Meehan has described the extreme variability of the corolla and calyx in this plant, and shows that it is dioecious. (7/12. "Variations in Epigaea repens" 'Proc. Acad.

Nat. Soc. of Philadelphia' May 1868 page 153.) It is much to be wished that the pollen-grains in the two male forms should be compared, and their fertilising power tried on the two female forms.

Ilex aquifolium (AQUIFOLIACEAE).

In the several works which I have consulted, one author alone says that the holly is dioecious. (7/13. Vaucher 'Hist. Phys. des Plantes d'Europe' 1841 tome 2 page 11.) During several years I have examined many plants, but have never found one that was really hermaphrodite. I mention this genus because the stamens in the female flowers, although quite dest.i.tute of pollen, are but slightly and sometimes not at all shorter than the perfect stamens in the male flowers. In the latter the ovary is small and the pistil is almost aborted. The filaments of the perfect stamens adhere for a greater length to the petals than in the female flowers. The corolla of the latter is rather smaller than that of the male. The male trees produce a greater number of flowers than the females.

Asa Gray informs me that I. opaca, which represents in the United States our common holly, appears (judging from dried flowers) to be in a similar state; and so it is, according to Vaucher, with several other but not with all the species of the genus.

GYNO-DIOECIOUS PLANTS.

The plants. .h.i.therto described either show a tendency to become dioecious, or apparently have become so within a recent period. But the species now to be considered consist of hermaphrodites and females without males, and rarely show any tendency to be dioecious, as far as can be judged from their present condition and from the absence of species having separated s.e.xes within the same groups. Species belonging to the present cla.s.s, which I have called gyno- dioecious, are found in various widely distinct families; but are much more common in the l.a.b.i.atae (as has long been noticed by botanists) than in any other group. Such cases have been noticed by myself in Thymus serpyllum and vulgaris, Satureia hortensis, Origanum vulgare, and Mentha hirsuta; and by others in Nepeta glechoma, Mentha vulgaris and aquatica, and Prunella vulgaris. In these two latter species the female form, according to H. Muller, is infrequent. To these must be added Dracocephalum Moldavic.u.m, Melissa officinalis and clinopodium, and Hyssopus officinalis. (7/14. H. Muller 'Die Befruchtung der Blumen' 1873 and 'Nature' 1873 page 161. Vaucher 'Plantes d'Europe' tome 3 page 611. For Dracocephalum Schimper as quoted by Braun 'Annals and Magazine of Natural History' 2nd series volume 18 1856 page 380. Lecoq 'Geographie Bot. de l'Europe' tome 8 pages 33, 38, 44, etc. Both Vaucher and Lecoq were mistaken in thinking that several of the plants named in the text are dioecious. They appear to have a.s.sumed that the hermaphrodite form was a male; perhaps they were deceived by the pistil not becoming fully developed and of proper length until some time after the anthers have dehisced.) In the two last-named plants the female form likewise appears to be rare, for I raised many seedlings of both, and all were hermaphrodites. It has already been remarked in the Introduction that andro-dioecious species, as they may be called, or those which consist of hermaphrodites and males, are extremely rare, or hardly exist.

Thymus serpyllum.

The hermaphrodite plants present nothing particular in the state of their reproductive organs; and so it is in all the following cases. The females of the present species produce rather fewer flowers and have somewhat smaller corollas than the hermaphrodites; so that near Torquay, where this plant abounds, I could, after a little practice, distinguish the two forms whilst walking quickly past them. According to Vaucher, the smaller size of the corolla is common to the females of most or all of the above-mentioned l.a.b.i.atae. The pistil of the female, though somewhat variable in length, is generally shorter, with the margins of the stigma broader and formed of more lax tissue, than that of the hermaphrodite. The stamens in the female vary excessively in length; they are generally enclosed within the tube of the corolla, and their anthers do not contain any sound pollen; but after long search I found a single plant with the stamens moderately exserted, and their anthers contained a very few full-sized grains, together with a mult.i.tude of minute empty ones. In some females the stamens are extremely short, and their minute anthers, though divided into the two normal cells or loculi, contained not a trace of pollen: in others again the anthers did not exceed in diameter the filaments which supported them, and were not divided into two loculi. Judging from what I have myself seen and from the descriptions of others, all the plants in Britain, Germany, and near Mentone, are in the state just described; and I have never found a single flower with an aborted pistil. It is, therefore, remarkable that, according to Delpino, this plant near Florence is generally trimorphic, consisting of males with aborted pistils, females with aborted stamens, and hermaphrodites. (7/15. 'Sull' Opera, la Distribuzione dei Sessi nelle Piante, etc' 1867 page 7. With respect to Germany H. Muller 'Die Befruchtung etc.' page 327.)

I found it very difficult to judge of the proportional number of the two forms at Torquay. They often grow mingled together, but with large patches consisting of one form alone. At first I thought that the two were nearly equal in number; but on examining every plant which grew close to the edge of a little overhanging dry cliff, about 200 yards in length, I found only 12 females; all the rest, some hundreds in number, being hermaphrodites. Again, on an extensive gently sloping bank, which was so thickly covered with this plant that, viewed from the distance of half a mile it appeared of a pink colour, I could not discover a single female. Therefore the hermaphrodites must greatly exceed in number the females, at least in the localities examined by me. A very dry station apparently favours the presence of the female form. With some of the other above-named l.a.b.i.atae the nature of the soil or climate likewise seems to determine the presence of one or both forms; thus with Nepeta glechoma, Mr. Hart found in 1873 that all the plants which he examined near Kilkenny in Ireland were females; whilst all near Bath were hermaphrodites, and near Hertford both forms were present, but with a preponderance of hermaphrodites. (7/16. 'Nature'

June 1873 page 162.) It would, however, be a mistake to suppose that the nature of the conditions determines the form independently of inheritance; for I sowed in the same small bed seeds of T. serpyllum, gathered at Torquay from the female alone, and these produced an abundance of both forms. There is every reason to believe, from large patches consisting of the same form, that the same individual plant, however much it may spread, always retains the same form. In two distant gardens I found ma.s.ses of the lemon-thyme (T. citriodorus, a var. of T. serpyllum, which I was informed had grown there during many years, and every flower was female.

With respect to the fertility of the two forms, I marked at Torquay a large hermaphrodite and a large female plant of nearly equal sizes, and when the seeds were ripe I gathered all the heads. The two heaps were of very nearly equal bulk; but the heads from the female plant numbered 160, and their seeds weighed 8.7 grains; whilst those from the hermaphrodite plant numbered 200, and their seeds weighed only 4.9 grains; so that the seeds from the female plant were to those from the hermaphrodite as 100 to 56 in weight. If the relative weight of the seeds from an equal number of flower-heads from the two forms be compared, the ratio is as 100 for the female to 45 for the hermaphrodite form.

Thymus vulgaris.

(FIGURE 7.15. Thymus vulgaris (magnified).

Left: Hermaphrodite.

Right: Two females.)

The common garden thyme resembles in almost every respect T. serpyllum. The same slight differences between the stigmas of the two forms could be perceived. In the females the stamens are not generally quite so much reduced as in the same form of T. serpyllum. In some specimens sent me from Mentone by Mr. Moggridge, together with the sketches in Figure 7.15, the anthers of the female, though small, were well formed, but they contained very little pollen, and not a single sound grain could be detected. Eighteen seedlings were raised from purchased seed, sown in the same small bed; and these consisted of seven hermaphrodites and eleven females. They were left freely exposed to the visits of bees, and no doubt every female flower was fertilised; for on placing under the microscope a large number of stigmas from female plants, not one could be found to which pollen-grains of thyme did not adhere. The seeds were carefully collected from the eleven female plants, and they weighed 98.7 grains; and those from the seven hermaphrodites 36.5 grains. This gives for an equal number of plants the ratio of 100 to 58; and we here see, as in the last case, how much more fertile the females are than the hermaphrodites. These two lots of seeds were sown separately in two adjoining beds, and the seedlings from both the hermaphrodite and female parent-plants consisted of both forms.

Satureia hortensis.

Eleven seedlings were raised in separate pots in a hotbed and afterwards kept in the greenhouse. They consisted of ten females and of a single hermaphrodite.

Whether or not the conditions to which they had been subjected caused the great excess of females I do not know. In the females the pistil is rather longer than that of the hermaphrodite, and the stamens are mere rudiments, with minute colourless anthers dest.i.tute of pollen. The windows of the greenhouse were left open, and the flowers were incessantly visited by humble and hive bees. Although the ten females did not produce a single grain of pollen, yet they were all thoroughly well fertilised by the one hermaphrodite plant, and this is an interesting fact. It should be added that no other plant of this species grew in my garden. The seeds were collected from the finest female plant, and they weighed 78 grains; whilst those from the hermaphrodite, which was a rather larger plant than the female, weighed only 33.2 grains; that is, in the ratio of 100 to 43. The female form, therefore, is very much more fertile than the hermaphrodite, as in the two last cases; but the hermaphrodite was necessarily self-fertilised, and this probably diminished its fertility.

We may now consider the probable means by which so many of the l.a.b.i.atae have been separated into two forms, and the advantages thus gained. H. Muller supposes that originally some individuals varied so as to produce more conspicuous flowers; and that insects habitually visited these first, and then dusted with their pollen visited and fertilised the less conspicuous flowers.

(7/17. 'Die Befruchtung der Blumen' pages 319, 326.) The production of pollen by the latter plants would thus be rendered superfluous, and it would be advantageous to the species that their stamens should abort, so as to save useless expenditure. They would thus be converted into females. But another view may be suggested: as the production of a large supply of seeds evidently is of high importance to many plants, and as we have seen in the three foregoing cases that the females produce many more seeds than the hermaphrodites, increased fertility seems to me the more probable cause of the formation and separation of the two forms. From the data above given it follows that ten plants of Thymus serpyllum, if half consisted of hermaphrodites and half of females, would yield seeds compared with ten hermaphrodite plants in the ratio of 100 to 72. Under similar circ.u.mstances the ratio with Satureia hortensis (subject to the doubt from the self-fertilisation of the hermaphrodite) would be as 100 to 60. Whether the two forms originated in certain individuals varying and producing more seed than usual, and consequently producing less pollen; or in the stamens of certain individuals tending from some unknown cause to abort, and consequently producing more seed, it is impossible to decide; but in either case, if the tendency to the increased production of seed were steadily favoured, the result would be the complete abortion of the male organs. I shall presently discuss the cause of the smaller size of the female corolla.

[Scabiosa arvensis (DIPSACEAE).

It has been shown by H. Muller that this species exists in Germany under an hermaphrodite and female form. (7/18. 'Die Befruchtung der Blumen' page 368. The two forms occur not only in Germany, but in England and France. Lecoq 'Geographie Bot.' 1857 tome 6 pages 473, 477, says that male plants as well as hermaphrodites and females coexist; it is, however, possible that he may have been deceived by the flowers being so strongly proterandrous. From what Lecoq says, S. succisa likewise appears to occur under two forms in France.) In my neighbourhood (Kent) the female plants do not nearly equal in number the hermaphrodites. The stamens of the females vary much in their degree of abortion; in some plants they are quite short and produce no pollen; in others they reach to the mouth of the corolla, but their anthers are not half the proper size, never dehisce, and contain but few pollen-grains, these being colourless and of small diameter. The hermaphrodite flowers are strongly proterandrous, and H. Muller shows that, whilst all the stigmas on the same flower-head are mature at nearly the same time, the stamens dehisce one after the other; so that there is a great excess of pollen, which serves to fertilise the female plants. As the production of pollen by one set of plants is thus rendered superfluous, their male organs have become more or less completely aborted. Should it be hereafter proved that the female plants yield, as is probable, more seeds than the hermaphrodites, I should be inclined to extend the same view to this plant as to the l.a.b.i.atae. I have also observed the existence of two forms in our endemic S. succisa, and in the exotic S. atro-purpurea. In the latter plant, differently to what occurs in S. arvensis, the female flowers, especially the larger circ.u.mferential ones, are smaller than those of the hermaphrodite form. According to Lecoq, the female flower-heads of S. succisa are likewise smaller than those of what he calls the male plants, but which are probably hermaphrodites.

Echium vulgare (BORAGINEAE).

The ordinary hermaphrodite form appears to be proterandrous, and nothing more need be said about it. The female differs in having a much smaller corolla and shorter pistil, but a well-developed stigma. The stamens are short; the anthers do not contain any sound pollen-grains, but in their place yellow incoherent cells which do not swell in water. Some plants were in an intermediate condition; that is, had one or two or three stamens of proper length with perfect anthers, the other stamens being rudimentary. In one such plant half of one anther contained green perfect pollen-grains, and the other half yellowish- green imperfect grains. Both forms produced seed, but I neglected to observe whether in equal numbers. As I thought that the state of the anthers might be due to some fungoid growth, I examined them both in the bud and mature state, but could find no trace of mycelium. In 1862 many female plants were found; and in 1864, 32 plants were collected in two localities, exactly half of which were hermaphrodites, fourteen were females, and two in an intermediate condition. In 1866, 15 plants were collected in another locality, and these consisted of four hermaphrodites and eleven females. I may add that this season was a wet one, which shows that the abortion of the stamens can hardly be due to the dryness of the sites where the plants grew, as I at one time thought probable. Seeds from an hermaphrodite were sown in my garden, and of the 23 seedlings raised, one belonged to the intermediate form, all the others being hermaphrodites, though two or three of them had unusually short stamens. I have consulted several botanical works, but have found no record of this plant varying in the manner here described.

Plantago lanceolata (PLANTAGINEAE).

Delpino states that this plant presents in Italy three forms, which graduate from an anemophilous into an entomophilous condition. According to H. Muller, there are only two forms in Germany, neither of which show any special adaptation for insect fertilisation, and both appear to be hermaphrodites.

(7/19. 'Die Befruchtung' etc. page 342.) But I have found in two localities in England female and hermaphrodite forms existing together; and the same fact has been noticed by others. (7/20. Mr. C.W. Crocker 'The Gardener's Chronicle' 1864 page 294. Mr. W. Marshall writes to me to the same effect from Ely.) The females are less frequent than the hermaphrodites; their stamens are short, and their anthers, which are of a brighter green whilst young than those of the other form, dehisce properly, yet contain either no pollen, or a small amount of imperfect grains of variable size. All the flower-heads on a plant belong to the same form. It is well known that this species is strongly proterogynous, and I found that the protruding stigmas of both the hermaphrodite and female flowers were penetrated by pollen-tubes, whilst their own anthers were immature and had not escaped out of the bud. Plantago media does not present two forms; but it appears from Asa Gray's description, that such is the case with four of the North American species. (7/21. 'Manual of the Botany of the Northern United States' 2nd edition 1856 page 269. See also 'American Journal of Science'

November 1862 page 419 and 'Proceedings of the American Academy of Science'

October 14, 1862 page 53.) The corolla does not properly expand in the short- stamened form of these plants.

Cnicus, Serratula, Eriophorum.

In the Compositae, Cnicus pal.u.s.tris and acaulis are said by Sir J.E. Smith to exist as hermaphrodites and females, the former being the more frequent. With Serratula tinctoria a regular gradation may be followed from the hermaphrodite to the female form; in one of the latter plants the stamens were so tall that the anthers embraced the style as in the hermaphrodites, but they contained only a few grains of pollen, and these in an aborted condition; in another female, on the other hand, the anthers were much more reduced in size than is usual.

Lastly, Dr. d.i.c.kie has shown that with Eriophorum angustifolium (Cyperaceae) hermaphrodite and female forms exist in Scotland and the Arctic regions, both of which yield seed. (7/22. Sir J.E. Smith 'Transactions of the Linnean Society'

volume 13 page 599. Dr. d.i.c.kie 'Journal of the Linnean Society Botany' volume 9 1865 page 161.)]

It is a curious fact that in all the foregoing polygamous, dioecious, and gyno- dioecious plants in which any difference has been observed in the size of the corolla in the two or three forms, it is rather larger in the females, which have their stamens more or less or quite rudimentary, than in the hermaphrodites or males. This holds good with Euonymus, Rhamnus catharticus, Ilex, Fragaria, all or at least most of the before-named l.a.b.i.atae, Scabiosa atro-purpurea, and Echium vulgare. So it is, according to Von Mohl, with Cardamine amara, Geranium sylvatic.u.m, Myosotis, and Salvia. On the other hand, as Von Mohl remarks, when a plant produces hermaphrodite flowers and others which are males owing to the more or less complete abortion of the female organs, the corollas of the males are not at all increased in size, or only exceptionally and in a slight degree, as in Acer. (7/23. 'Botanische Zeitung' 1863 page 326.) It seems therefore probable that the decreased size of the female corollas in the foregoing cases is due to a tendency to abortion spreading from the stamens to the petals. We see how intimately these organs are related in double flowers, in which the stamens are readily converted into petals. Indeed some botanists believe that petals do not consist of leaves directly metamorphosed, but of metamorphosed stamens. That the lessened size of the corolla in the above case is in some manner an indirect result of the modification of the reproductive organs is supported by the fact that in Rhamnus catharticus not only the petals but the green and inconspicuous sepals of the female have been reduced in size; and in the strawberry the flowers are largest in the males, mid-sized in the hermaphrodites, and smallest in the females. These latter cases,--the variability in the size of the corolla in some of the above species, for instance in the common thyme,--together with the fact that it never differs greatly in size in the two forms--make me doubt much whether natural selection has come into play;--that is whether, in accordance with H. Muller's belief, the advantage derived from the polleniferous flowers being visited first by insects has been sufficient to lead to a gradual reduction of the corolla of the female.