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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 Darwin, who kindly sent it to me from his yet unpublished MS.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. bluttaria 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 spocies. 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 "heltrochromatic" 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.

Kelative Fertility Op The EToMocnROMatic And Heterociiromatic

Unions.

1. V. phceniceum by its own pollen, . . . 1000

2. V. phaeniceum, rosea, by pollen of V. phceniceum, ... 958

3. V. phceniceum, alba, by pollen of V. phceniceum, rosea, 8(J7

4. V. phceniceum, alba, by pollen of V. phceniceum, . ... 785

5. V. phceniceum, by pollen of V.phceniceum, rosta, . ... 680

6. V. phceniceum, by pollen of V. phceniceum, alba, ... 563

7. V. lychnitis, alba, by pollen of V. lychnitis, lutea, ... 822

8. V. lychnitis, lutea, by pollen of V. lychnitis, alba, . ... 944

9. V. blattaria, alba, by pollen of V. blattaria, lutea, ... 792

10. V. blattaria, lutea, by pollen of V. blaltaria, alba, ... 969

11. V. thapsus, lutea, by pollen of V. thapstix, alba, . ... 947 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. phceniceum and its varieties are in each case to be considered relatively to the assumed results of the pure unions of V. phceniceum given in Table 2, these plants experimented upon being individually self-sterile as shown in Table 1. The anions, 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, aud 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 p with yellow 3, distinct from those of yellow as p with white as cj, 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 nro 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 tact announced by Gartner, that varieties of a species, characterised by no other differences than that of colour, arc occasionally so differentiated functionally, that the cross-unions, as compared with the fertility of the puro unions, invariably indicate a certain degree of sterilisation!

In connection with this higher relative fertility of homochromatic to that of In terochromatie unions, as limited to the crossing of varieties of a single species, I will venture to add that this law not only holJs, but, ai I believe, extends t,o 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, wo 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 rod; 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, phevnieeum and varieties given in Table 1. Thus the V. phoeniccum 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. phecniceuut 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 2G, 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 mse-colourcd 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.

Gartner'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 Gartner shows* that on the calculation of V. lychnitis, fl'. alia, yielding with its own pollen 1.000 seeds, it yields when fertilised with the pollen of V. Ualtaria ft. alba, 0.622 seeds, and with that of V. blattaria, fl. luiea, 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 ns now see then in how far this law of the differences in the fertility of the homochrouiatic 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 homochrouiatic and the heterochromatic unions, in each case, by making calculations from an assumed 100 seeds produced by the more fertile of the two r.nions 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 honiochromatic unions, or those in which similarly colour* Vorsuche uber dio Bastartlorzeugunj, 1849, section 21G.

ed flowers are the more fertile: and lastly, the irregnlar unions in which no relations are observed between the degree of fertility aud affinity of colours.

[table]

ranged those unions in which a certain regularity is observed between the colour relationship and the degree of fertility. Now, by comparing the 14 unions therein given, we find that the heterocbr)matic unions are, in the greater number of cases, more fertile, viz., as 8 to 6, than the homochromatic unions, and that this higher fertility, in every case, results from those unions in which the yellow variety of the species is treated as female. Again that the average proportion of the four heterociiromatic to the four converso homoehromstie unions in the first of the above tables is nearly as 7 to 6 is favour of the former. In B. 2 of the tabulated results, we see in oue

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