The Different Forms of Flowers on Plants of the Same Species Part 19

From the three forms occurring in approximately equal numbers in a state of nature, and from the results of sowing seed naturally produced, there is reason to believe that each form, when legitimately fertilised, reproduces all three forms in about equal numbers. Now, we have seen (and the fact is a very singular one) that the fifty-six plants produced from the long-styled form, illegitimately fertilised with pollen from the same form (Cla.s.s 1 and 2), were all long-styled. The short-styled form, when self-fertilised (Cla.s.s 3), produced eight short-styled and one long-styled plant; and the mid-styled form, similarly treated (Cla.s.s 4), produced three mid-styled and one long-styled offspring; so that these two forms, when illegitimately fertilised with pollen from the same form, evince a strong, but not exclusive, tendency to reproduce the parent-form.

When the short-styled form was illegitimately fertilised by the long-styled form (Cla.s.s 5), and again when the mid-styled was illegitimately fertilised by the long-styled (Cla.s.s 6), in each case the two parent-forms alone were reproduced.

As thirty-seven plants were raised from these two unions, we may, with much confidence, believe that it is the rule that plants thus derived usually consist of both parent-forms, but not of the third form. When, however, the mid-styled form was illegitimately fertilised by the longest stamens of the short-styled (Cla.s.s 7), the same rule did not hold good; for the seedlings consisted of all three forms. The illegitimate union from which these latter seedlings were raised is, as previously stated, singularly fertile, and the seedlings themselves exhibited no signs of sterility and grew to their full height. From the consideration of these several facts, and from a.n.a.logous ones to be given under Oxalis, it seems probable that in a state of nature the pistil of each form usually receives, through the agency of insects, pollen from the stamens of corresponding height from both the other forms. But the case last given shows that the application of two kinds of pollen is not indispensable for the production of all three forms. Hildebrand has suggested that the cause of all three forms being regularly and naturally reproduced, may be that some of the flowers are fertilised with one kind of pollen, and others on the same plant with the other kind of pollen. Finally, of the three forms, the long-styled evinces somewhat the strongest tendency to reappear amongst the offspring, whether both, or one, or neither of the parents are long-styled.

[TABLE 5.30. Tabulated results of the fertility of the foregoing illegitimate plants, when legitimately fertilised, generally by illegitimate plants, as described under each experiment. Plants 11, 12 and 13 are excluded, as they were illegitimately fertilised.

NORMAL STANDARD OF FERTILITY OF THE THREE FORMS, WHEN LEGITIMATELY AND NATURALLY FERTILISED.

Column 1: Form.

Column 2: Average number of seeds per capsule.

Column 3: Maximum number in any one capsule.

Column 4: Minimum number in any one capsule.

Long-styled : 93 : 159 : No record was kept as all very poor capsules were rejected.

Mid-styled : 130 : 151 : No record was kept as all very poor capsules were rejected.

Short-styled : 83.5 : 112 : No record was kept as all very poor capsules were rejected.

TABLE 5.30. Continued.

CLa.s.s 1 AND CLa.s.s 2.--ILLEGITIMATE PLANTS RAISED FROM LONG-STYLED PARENTS FERTILISED WITH POLLEN FROM OWN-FORM MID-LENGTH OR SHORTEST STAMENS.

Column 1: Number (name) of plant.

Column 2: Form.

Column 3: Average number of seeds per capsule.

Column 4: Maximum number of seeds in any one capsule.

Column 5: Minimum number of seeds in any one capsule.

Column 6: Average number of seeds, expressed as the percentage of the normal standard.

1 : Long-styled : 0 : 0 : 0 : 0.

2 : Long-styled : 4.5 : ? : 0 : 5.

3 : Long-styled : 4.5 : ? : 0 : 5.

4 : Long-styled : 4.5 : ? : 0 : 5.

5 : Long-styled : 0 or 1 : 2 : 0 : 0 or 1.

6 : Long-styled : 0 : 0 : 0 : 0.

7 : Long-styled : 36.1 : 47 : 22 : 39.

8 : Long-styled : 41.1 : 73 : 11 : 44.

9 : Long-styled : 57.1 : 86 : 23 : 61.

10 : Long-styled : 44.2 : 69 : 25 : 47.

CLa.s.s 3. ILLEGITIMATE PLANTS RAISED FROM SHORT-STYLED PARENTS FERTILISED WITH POLLEN FROM OWN-FORM SHORTEST STAMENS.

14 : Short-styled : 28.3 : 51 : 11 : 33.

15 : Short-styled : 32.6 : 49 : 20 : 38.

16 : Short-styled : 77.8 : 97 : 60 : 94.

17 : Long-styled : 76.3 : 88 : 57 : 82.

CLa.s.s 4. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH POLLEN FROM OWN-FORM LONGEST STAMENS.

18 : Mid-styled : 102.6 : 131 : 63 : 80.

19 : Mid-styled : 73.4 : 87 : 64 : 56.

20 : Long-styled : 69.6 : 83 : 52 : 75.

CLa.s.s 5. ILLEGITIMATE PLANTS RAISED FROM SHORT-STYLED PARENTS FERTILISED WITH POLLEN FROM THE MID-LENGTH STAMENS OF THE LONG-STYLED FORM.

21 : Short-styled : 43.0 : 63 : 26 : 52.

22 : Short-styled : 100.5 : 123 : 86 : 121.

23 : Short-styled : 113.5 : 123 : 93 : 136.

24 : Long-styled : 82.0 : 120 : 67 : 88.

25 : Long-styled : 122.5 : 149 : 84 : 131.

CLa.s.s 6. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH POLLEN FROM THE SHORTEST STAMENS OF THE LONG-STYLED FORM.

26 : Mid-styled : 86.0 : 109 : 61 : 66.

27 : Mid-styled : 99.4 : 122 : 53 : 76.

28 : Mid-styled : 89.0 : 119 : 69 : 68.

29 : Long-styled : 100.0 : 121 : 77 : 107.

30 : Long-styled : 94.0 : 106 : 66 : 101.

31 : Long-styled : 90.6 : 97 : 79 : 98.

CLa.s.s 7. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH POLLEN FROM THE LONGEST STAMENS OF THE SHORT-STYLED FORM.

32 : Mid-styled : 127.2 : 144 : 96 : 98.

33 : Short-styled : 113.9 : 137 : 90 : 137.

The lessened fertility of most of these illegitimate plants is in many respects a highly remarkable phenomenon. Thirty-three plants in the seven cla.s.ses were subjected to various trials, and the seeds carefully counted. Some of them were artificially fertilised, but the far greater number were freely fertilised (and this is the better and natural plan) through the agency of insects, by other illegitimate plants. In the right hand, or percentage column, in Table 5.30, a wide difference in fertility between the plants in the first four and the last three cla.s.ses may be perceived. In the first four cla.s.ses the plants are descended from the three forms illegitimately fertilised with pollen taken from the same form, but only rarely from the same plant. It is necessary to observe this latter circ.u.mstance; for, as I have elsewhere shown, most plants, when fertilised with their own pollen, or that from the same plant, are in some degree sterile, and the seedlings raised from such unions are likewise in some degree sterile, dwarfed, and feeble. (5/3. 'The Effects of Cross and Self- fertilisation in the Vegetable Kingdom' 1876.) None of the nineteen illegitimate plants in the first four cla.s.ses were completely fertile; one, however, was nearly so, yielding 96 per cent of the proper number of seeds. From this high degree of fertility we have many descending gradations, till we reach an absolute zero, when the plants, though bearing many flowers, did not produce, during successive years, a single seed or even seed-capsule. Some of the most sterile plants did not even yield a single seed when legitimately fertilised with pollen from legitimate plants. There is good reason to believe that the first seven plants in Cla.s.s 1 and 2 were the offspring of a long-styled plant fertilised with pollen from its own-form shortest stamens, and these plants were the most sterile of all. The remaining plants in Cla.s.s 1 and 2 were almost certainly the product of pollen from the mid-length stamens, and although very sterile, they were less so than the first set. None of the plants in the first four cla.s.ses attained their full and proper stature; the first seven, which were the most sterile of all (as already stated), were by far the most dwarfed, several of them never reaching to half their proper height. These same plants did not flower at so early an age, or at so early a period in the season, as they ought to have done. The anthers in many of their flowers, and in the flowers of some other plants in the first six cla.s.ses, were either contabescent or included numerous small and shrivelled pollen-grains. As the suspicion at one time occurred to me that the lessened fertility of the illegitimate plants might be due to the pollen alone having been affected, I may remark that this certainly was not the case; for several of them, when fertilised by sound pollen from legitimate plants, did not yield the full complement of seeds; hence it is certain that both the female and male reproductive organs were affected. In each of the seven cla.s.ses, the plants, though descended from the same parents, sown at the same time and in the same soil, differed much in their average degree of fertility.

Turning now to the fifth, sixth, and seventh cla.s.ses, and looking to the right hand column of Table 5.30, we find nearly as many plants with a percentage of seeds above the normal standard as beneath it. As with most plants the number of seeds produced varies much, it might be thought that the present case was one merely of variability. But this view must be rejected, as far as the less fertile plants in these three cla.s.ses are concerned: first, because none of the plants in Cla.s.s 5 attained their proper height, which shows that they were in some manner affected; and, secondly, because many of the plants in Cla.s.ses 5 and 6 produced anthers which were either contabescent or included small and shrivelled pollen-grains. And as in these cases the male organs were manifestly deteriorated, it is by far the most probable conclusion that the female organs were in some cases likewise affected, and that this was the cause of the reduced number of seeds.

With respect to the six plants in these three cla.s.ses which yielded a very high percentage of seeds, the thought naturally arises that the normal standard of fertility for the long-styled and short-styled forms (with which alone we are here concerned) may have been fixed too low, and that the six legitimate plants are merely fully fertile. The standard for the long-styled form was deduced by counting the seeds in twenty-three capsules, and for the short-styled form from twenty-five capsules. I do not pretend that this is a sufficient number of capsules for absolute accuracy; but my experience has led me to believe that a very fair result may thus be gained. As, however, the maximum number observed in the twenty-five capsules of the short-styled form was low, the standard in this case may possibly be not quite high enough. But it should be observed, in the case of the illegitimate plants, that in order to avoid over-estimating their infertility, ten very fine capsules were always selected; and the years 1865 and 1866, during which the plants in the three latter cla.s.ses were experimented on, were highly favourable for seed-production. Now, if this plan of selecting very fine capsules during favourable seasons had been followed for obtaining the normal standards, instead of taking, during various seasons, the first capsules which came to hand, the standards would undoubtedly have been considerably higher; and thus the fact of the six foregoing plants appearing to yield an unnaturally high percentage of seeds may, perhaps, be explained. On this view, these plants are, in fact, merely fully fertile, and not fertile to an abnormal degree. Nevertheless, as characters of all kinds are liable to variation, especially with organisms unnaturally treated, and as in the four first and more sterile cla.s.ses, the plants derived from the same parents and treated in the same manner, certainly did vary much in sterility, it is possible that certain plants in the latter and more fertile cla.s.ses may have varied so as to have acquired an abnormal degree of fertility. But it should be noticed that, if my standards err in being too low, the sterility of all the many sterile plants in the several cla.s.ses will have to be estimated by so much the higher. Finally, we see that the illegitimate plants in the four first cla.s.ses are all more or less sterile, some being absolutely barren, with one alone almost completely fertile; in the three latter cla.s.ses, some of the plants are moderately sterile, whilst others are fully fertile, or possibly fertile in excess.

The last point which need here be noticed is that, as far as the means of comparison serve, some degree of relations.h.i.+p generally exists between the infertility of the illegitimate union of the several parent-forms and that of their illegitimate offspring. Thus the two illegitimate unions, from which the plants in Cla.s.ses 6 and 7 were derived, yielded a fair amount of seed, and only a few of these plants are in any degree sterile. On the other hand, the illegitimate unions between plants of the same form always yield very few seeds, and their seedlings are very sterile. Long-styled parent-plants when fertilised with pollen from their own-form shortest stamens, appear to be rather more sterile than when fertilised with their own-form mid-length stamens; and the seedlings from the former union were much more sterile than those from the latter union. In opposition to this relations.h.i.+p, short-styled plants illegitimately fertilised with pollen from the mid-length stamens of the long- styled form (Cla.s.s 5) are very sterile; whereas some of the offspring raised from this union were far from being highly sterile. It may be added that there is a tolerably close parallelism in all the cla.s.ses between the degree of sterility of the plants and their dwarfed stature. As previously stated, an illegitimate plant fertilised with pollen from a legitimate plant has its fertility slightly increased. The importance of the several foregoing conclusions will be apparent at the close of this chapter, when the illegitimate unions between the forms of the same species and their illegitimate offspring, are compared with the hybrid unions of distinct species and their hybrid offspring.

OXALIS.

No one has compared the legitimate and illegitimate offspring of any trimorphic species in this genus. Hildebrand sowed illegitimately fertilised seeds of Oxalis Valdiviana, but they did not germinate (5/4. 'Botanische Zeitung' 1871 page 433 footnote.); and this fact, as he remarks, supports my view that an illegitimate union resembles a hybrid one between two distinct species, for the seeds in this latter case are often incapable of germination.

[The following observations relate to the nature of the forms which appear among the legitimate seedlings of Oxalis Valdiviana. Hildebrand raised, as described in the paper just referred to, 211 seedlings from all six legitimate unions, and the three forms appeared among the offspring from each union. For instance, long-styled plants were legitimately fertilised with pollen from the longest stamens of the mid-styled form, and the seedlings consisted of 15 long-styled, 18 mid-styled, and 6 short-styled. We here see that a few short-styled plants were produced, though neither parent was short-styled; and so it was with the other legitimate unions. Out of the above 211 seedlings, 173 belonged to the same two forms as their parents, and only 38 belonged to the third form distinct from either parent. In the case of O. Regnelli, the result, as observed by Hildebrand, was nearly the same, but more striking: all the offspring from four of the legitimate unions consisted of the two parent-forms, whilst amongst the seedlings from the other two legitimate unions the third form appeared. Thus, of the 43 seedlings from the six legitimate unions, 35 belonged to the same two forms as their parents, and only 8 to the third form. Fritz Muller also raised in Brazil seedlings from long-styled plants of O. Regnelli legitimately fertilised with pollen from the longest stamens of the mid-styled form, and all these belonged to the two parent-forms. (5/5. 'Jenaische Zeitschrift' etc. Band 6 1871 page 75.) Lastly, seedlings were raised by me from long-styled plants of O. speciosa legitimately fertilised by the short-styled form, and from the latter reciprocally fertilised by the long-styled; and these consisted of 33 long-styled and 26 short-styled plants, with not one mid-styled form. There can, therefore, be no doubt that the legitimate offspring from any two forms of Oxalis tend to belong to the same two forms as their parents; but that a few seedlings belonging to the third form occasionally make their appearance; and this latter fact, as Hildebrand remarks, may be attributed to atavism, as some of their progenitors will almost certainly have belonged to the third form.

When, however, any one form of Oxalis is fertilised illegitimately with pollen from the same form, the seedlings appear to belong invariably to this form. Thus Hildebrand states that long-styled plants of O. rosea growing by themselves have been propagated in Germany year after year by seed, and have always produced long-styled plants. (5/6. 'Ueber den Trimorphismus in der Gattung Oxalis: Monatsberichte der Akad. der Wissen. zu Berlin' 21 June 1866 page 373 and 'Botanische Zeitung' 1871 page 435.) Again, 17 seedlings were raised from mid- styled plants of O. hedysaroides growing by themselves, and these were all mid- styled. So that the forms of Oxalis, when illegitimately fertilised with their own pollen, behave like the long-styled form of Lythrum salicaria, which when thus fertilised always produced with me long-styled offspring.]

PRIMULA.

Primula Sinensis.

I raised during February 1862, from some long-styled plants illegitimately fertilised with pollen from the same form, twenty-seven seedlings. These were all long-styled. They proved fully fertile or even fertile in excess; for ten flowers, fertilised with pollen from other plants of the same lot, yielded nine capsules, containing on an average 39.75 seeds, with a maximum in one capsule of 66 seeds. Four other flowers legitimately crossed with pollen from a legitimate plant, and four flowers on the latter crossed with pollen from the illegitimate seedlings, yielded seven capsules with an average of 53 seeds, with a maximum of 72. I must here state that I have found some difficulty in estimating the normal standard of fertility for the several unions of this species, as the results differ much during successive years, and the seeds vary so greatly in size that it is hard to decide which ought to be considered good. In order to avoid over- estimating the infertility of the several illegitimate unions, I have taken the normal standard as low as possible.

From the foregoing twenty-seven illegitimate plants, fertilised with their own- form pollen, twenty-five seedling grandchildren were raised; and these were all long-styled; so that from the two illegitimate generations fifty-two plants were raised, and all without exception proved long-styled. These grandchildren grew vigorously, and soon exceeded in height two other lots of illegitimate seedlings of different parentage and one lot of equal-styled seedlings presently to be described. Hence I expected that they would have turned out highly ornamental plants; but when they flowered, they seemed, as my gardener remarked, to have gone back to the wild state; for the petals were pale-coloured, narrow, sometimes not touching each other, flat, generally deeply notched in the middle, but not flexuous on the margin, and with the yellow eye or centre conspicuous.

Altogether these flowers were strikingly different from those of their progenitors; and this I think, can only be accounted for on the principle of reversion. Most of the anthers on one plant were contabescent. Seventeen flowers on the grandchildren were illegitimately fertilised with pollen taken from other seedlings of the same lot, and produced fourteen capsules, containing on an average 29.2 seeds; but they ought to have contained about 35 seeds. Fifteen flowers legitimately fertilised with pollen from an illegitimate short-styled plant (belonging to the lot next to be described) produced fourteen capsules, containing an average of 46 seeds; they ought to have contained at least 50 seeds. Hence these grandchildren of illegitimate descent appear to have lost, though only in a very slight degree, their full fertility.