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though much more closely allied to the V. thapsus than the others given in Table, are nevertheless least effective in their conjunctive fertility with the latter species. Furthermore, we see by those unions of V. thapsus, lutea, as female, with the yellow and white varieties of V. lychnitis, and of V. pyramidatum; that though the pollen of V. pyramidatum is equally potent on the stigma of V. thapsus lutea, as is that of V. lychnitis, alba, there is nevertheless a considerable decrease in the proportionate fertility of the unions with V. lychnitis, lutea. Hence, as we have before shown it to be with the varieties of V. phoniceum, and judging by the physiological test, the V. pyramidatum would interpolate itself between these slightly different and undoubted varieties of a species.

In the foregoing Tables, then, I have given nearly all the results of my experiments in the unions of Verbasca. Before considering the nature of the evidence they afford us as to the relationship of mongrelism and hybridism, I will briefly attempt to show how far these results accord with those of Gartner, who has also largely experimented on these plants. I may premise, however, that as my experiments are much less numerous than Gartner's, comprising some 57 distinct unions, in which 527 flowers were artificially fertilised,—whereas, as will be seen beneath, Gartner subjected no less than 1085 flowers to experiment, they would induce very different conclusions, in certain points, to those arrived at by that careful experimentalist. I readily acknowledge therefore the higher claim of the latter to a provisional acceptance, until further experiments show more conclusively their relative correctness. I have also to notice a cause of some little discordance in such a comparative examination as that which I am about to institute; namely, that I have given in every case the average number of seeds produced both by pure and mixed unions, whereas Gartner gives the average number of seeds in the pure unions only, taking in each case the maximum or highest number produced by a single capsule in the mixed unions. I was not aware of this peculiarity in Gartner's deductions when I counted the seeds in my own experiments, otherwise, I should have drawn them up for the sake of comparison on a similar basis; even though I consider it a less fair method than that which I have adopted, in all such cases as the present, in which the ovaries

contain an indefinite number of ovules. And this the more especially if, as in my own experiments, castration and artificial impregnation be performed in both pure and mixed unions. In drawing comparisons between uncastrated pure unions, and castrated mixed unions, the average of the former, with the maximum of the latter would certainly be the fairer method, as affording a complement for the sterilising influence of castration.

For the following digest of Gartner's experiments I have to thank Mr. Darwin, who kindly sent it to me from his yet unpublished MS. illustrations of these phenomena: "To show the scale on which Gartner worked, I may state that, in the genus Verbascum, he crossed no less than 1085 flowers and counted their seed, and recorded the results. Now in two of his works he distinctly asserts that similarly coloured varieties of V. lychnitis and V. blattaria are more fertile together than when differently coloured varieties of the same species are crossed. But Gartner chiefly relied on the crosses which he made between the yellow and white varieties of these two species and nine other distinct species, and he asserts that the white-flowering species yielded more seed than did the yellow-flowered varieties when crossed with the same white varieties of these two-flowered species, and so conversely with the yellow flowering varieties with the yellow species. The general results may be seen in his Table. In one case he gives the following details; the white Verbascum lychnitis naturally fertilised with its own pollen had on an average in 12 capsules 96 good seeds: 20 flowers artificially fertilised with the pollen of its yellow variety gave as the maximum 89 good seeds. I should have thought that this slight difference might have been wholly due to the evil effects of castration; but Gartner shows that the white variety of V. lychnitis, fertilised by the pollen of the white and yellow varieties of V. blattaria, in both of which cases there must have been previous castration, bore seeds to the white variety in the proportion of 62, to 43 when pollen of the yellow variety was used."

First then, in regard to the greater fertility of the unions of similarily coloured varieties, relatively to that of the unions of dissimilarly coloured varieties of the same species. To these phenomena I will apply in the subsequent parts of this paper the following terms: "Homochromatic" to the unions of similarly coloured varieties, and "hetero

chromatic" to those in which dissimilarly coloured varieties are united In the following table we will at once see the comparative fertility

of these different unions given in the previous ones.

RELATIVE FERTILITY OF THE HOMOCHROMATIC AND HETEROCHROMATIC

UNIONS.

1. V. phoeniceum by its own pollen,

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1000

958

...

867

735

680

563

822

...

944

...

792

969

...

947

...

2. V. phœniceum, rosea, by pollen of V. phoeniceum, 3. V. phoeniceum, alba, by pollen of V. phæniceum, rosea, 4. V. phæniceum, alba, by pollen of V. phaniceum, . 5. V. phæniceum, by pollen of V. phœniceum, ros?a, 6. V. phoeniceum, by pollen of V. phœniceum, alba, 7. V. lychnitis, alba, by pollen of V. lychnitis, lutea, 8. V. lychniits, lutea, by pollen of V. lychnitis, alba, . 9. V. blattaria, alba, by pollen of V. blattaria, lutea, 10. V. blattaria, lutea, by pollen of V. blattaria, alba, 11. V. thapsus, lutea, by pollen of V. thapsus, alba, Here the comparative fertility is shown by calculation from the number of seeds produced by 20 assumed capsules of both unions. The various cross-unions of V. phæniceum and its varieties are in each case to be considered relatively to the assumed results of the pure unions of V. phoeniceum given in Table 2, these plants experimented upon being individually self-sterile as shown in Table 1. The unions, on the other hand, of V. lychnitis, blattaria, and thapsus, with their respective varieties, are each to be considered relatively to the 1000 seeds produced by the pure union of that variety given as female. Now in all the above heterochromatic unions, as compared with the homochromatic, we have the clearest evidence of reduced fertility. Thus, taking the 10 heterochromatic unions given, and comparing them with a similiar number of homochromatic unions, we find that the average proportion in which the former exceeds the latter, is as '05 to 23. On again confining ourselves to those species alone which have the yellow and white varieties, and keeping the unions of white as with yellow ♂, distinct from those of yellow as 2 with white as 3, we find that

the cross-unions with white as female are to the pure unions of the latter as 04 to 28; and in those cross-unions with yellow as female,

the proportions are as 23 to 29, relatively to the pure unions of the latter. Thus, in whatever way we proceed, the general results are the same, testifying to the highly remarkable fact announced by Gärtner, that varieties of a species, characterised by no other differences than that of colour, are occasionally so differentiated functionally, that the cross-unions, as compared with the fertility of the pure unions, invariably indicate a certain degree of sterilisation!

In connection with this higher relative fertility of homochromatic to that of heterochromatic unions, as limited to the crossing of varieties of a single species, I will venture to add that this law not only holds, but, as I believe, extends to and regulates the functional relations in accordance with the relative colour affinities of the varieties crossed. Thus for the sake of illustration, we may take the three primary colours of the cyanic series, namely, blue, violet, and red. Now beginning with red, we know that greater physiological changes must take place in the minute anatomy of the petals of an originally red-coloured flower to give the impression of blue than that of violet. Hence we might suspect that a species presenting varieties characterised by such differences in colour, would likewise afford different degrees of fertility in their conjunctive functional relations, the blue and red yielding less fertile unions, than the violet and red; while the violet holding an intermediate colour position between these, might be equally as fertile in its unions with the blue as the red variety. In practical illustration of these relations, we may take the results of the various unions of V. phæniceum and varieties given in Table 1. Thus the V. phoniceum with purplish-violet flowers yields more seeds when fertilised by the pollen of the rose-coloured variety, than by that of the white variety, in the proportion of 5 to 4. Again the white variety of V. phoniceum fertilised by the pollen of the rose variety yields an average of 29 seeds per capsule, and by that of the purplish violet variety the average per capsule is 26, that is as 9 to 8, in favour of the unions of the rose and white varieties. We see here evident co-relations between the degrees of fertility and the colour affinities of these plants in their respective sexual unions, and I venture to look for more marked differences in these respects, had we as subjects of experiment,

varieties of a species presenting three, or at least two, of the primary colours with intermediate shades irrespective of the white. The latter being rather unsatisfactory from its similar relations to the primary colours, though in such instances as the above of the purplish-violet, rose and white, in which we have secondary colours forming intermediate steps between the primary and white, by a gradual dilution of the colouring principle, we find that the white, agreeably to the above views, form less fertile conjunctions with the violet than the rose-coloured flowers. Before passing from this point of my subject, I will now only add that I have thought these indications of a tangible law, co-relating and regulating the sexual functions of varieties when crossed-dim though they as yet undoubtedly are worth noticing, as we are as yet in utter ignorance of anything like definite or specific laws in these phenomena, the results being considered as most capricious and uncertain.

Gärtner's second proposition is, that in the hybridism of differently coloured varieties of distinct species of Verbasca, the conjunctions of the similarly coloured flowers are more fertile than these of dissimilarly coloured flowers. For example Gärtner shows that on the calculation of V. lychnitis, fl. alba, yielding with its own pollen 1.000 seeds, it yields when fertilised with the pollen of V. blattaria fl. alba, 0.622 seeds, and with that of V. blattaria, f. lutea, only 0.438, so that the similarly coloured unions of these species are more fertile than the dissimilarly coloured unions in the proportion of 3 to 2. Let us now see then in how far this law of the differences in the fertility of the homochromatic relatively to the heterochromatic unions, is borne out in the case of my own experiments as given in the preceding Tables. And here again, for the sake of clearness, and facility of reference, I will restate them in a tabular form, and show as clearly as possible the differences in the relative fertility of the homochromatic and the heterochromatic unions, in each case, by making calculations from an assumed 100 seeds produced by the more fertile of the two rnions compared. The results may be conveniently arranged under three heads; thus, first, the heterochromatic unions, or those in which the unions of differently coloured flowers are the more fertile: second, the homochromatic unions, or those in which similarly colour

* Versuche über die Bastarderzeugunj, 1849, section 216.

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