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The results of experiments on the V. blattaria, varieties lutea and alba. are given in the above Tables: they comprise 12 unions between the white and yellow varieties of three species. Let us briefly compare the results of their reciprocal unions. First, the fertility of V. blattaria, alba, when fertilised by its own pollen. undergoes the highly proportionate sterilisation of 98 : 78 when fertilised with the pollen of the yellow variety—V. blattaria, lutea. In the converse case, the sterilising influence of the cross relatively to the pure unions of these forms is much decreased, the pure union of V. blattaria, lutea, yielding more seed in the proportions of 90 : 88 than from its cross-union with the white variety—V. blattaria, alba. Secondly, as to the hybrid unions with the pollens of the yellow and white varieties of V. thapsus. In these the pollen of the white variety is the more potent. Thus V. blattaria, alba, fertilised by pollen of V. thapsus, alba, affords an average fertility of 43, whereas by that of V. thapsus, lutea, the produce is reduced to 32, relatively in both cases to 100, the average fertility of V. blattaria, alba, when fertilised by its own pollen. liy the union of the yellow and white varieties of V. thapsus with the yellow variety of V. blattaria, we see that the relative differences in tho potency of the two pollens on the stigmas of V. blattaria, lutea, are much less than those we have above noticed when V. blattaria alba is used as female; and also that the potency of the two pollens is greater on the stigmas of the yellow than those of the white variety of V. blattaria lutca; and again that the white variety of V. thapsus is more fertile than the yellow, in their respective unions with the V. blattaria, alba. Thus V. blattaria, lutea, by pollen of V. thapsus, alba, gives an average fertility of 61 ; by pollen of V. thapsus, lutea, 50, relatively to 90, the product of fertilisation by its own pollen. Lastly, wo have the different unions of the two pollens of the white and yellow V. lyclmilis on the stigmas of the yellow and white varieties of V. blattaria. In these unions we see first that with V. blattaria, alba as female, the pollen of the white variety exceeds that of the yellow in the proportion of 36 : 23; secondly, with the V. blattaria, lutea, as female, the pollen of the white variety is again singularly enough the more fertile, exceeding that of the yellow variety, in the proportion of 45 : 41. Thirdly, we find that here also the yellow variety of V. blattaria yields a higher degree of fertility,—taking the conjoint products of the two unions with the pollen respectively of V. thapsus, lutea and alba,—than the white variety of V. blattaria when similarly treated, the proportions being as 70 of the V. blattaria to 47 of the V. blattaria, alba, or nearly as 3 : 2.
This leads me to notice a curious fact prominently brought before us in the above Table, whatever may be its real signification, namely, that the yellow varieties of V. lychnitis and blattaria, though yielding a higher grade of fertility to the pollen of the white and yellow varieties of distinct species than do the respective white varieties of the above species when similarly fertilised, are nevertheless less productive of seed than the white, when both are fertilised with their own pollen. This will be seen by consulting the following tabular arrangement, in which I have given a reduced approximate of the relative fertility of the different unions, selecting from the hybrid unions in each instance only the most fertile.
1. V. lychnitis, alba, by own pollen is as 83 : 75 of V. lychnitis, lutca, by its own pollen.
2. V. lychnitis, alba, by pollen of V. lychnitis, lutea, is as 68 : 71 of V. lychnitis, lutca, by pollen of V. lychnitis, alba.
3. F. lychnitis, alia, by pollen V. thapsus, alba, is as 39 : 30 of V. lychnitis, lutea, by pollen of V. thapsus, alba.
4. F. lychnitis, alba, by pollen of V. phceniceum, alba as 56 : 42 of V. lychnitis, lutea, by pollen of V. phamiceum, alba.
f>. V. blattaria, alba, by its own pollen, is as 98 : 90 of F. blattaria, lutea by its own pollen.
6. V. blattaria, lutea, by pollen of V. blattaria, alba is as 96 : 79 of V. blattaria, alba, by pollen of V. blattaria, lutea.
7. V. blattaria, lutea, by pollen of F. thapsus, alba, as 61 : 43 of V. blattaria, alba, by pollen of V. thapsus, alba.
8. V. blattaria, lutea by pollen of V. lychnitis, alba, as 45 : 36 of V. blattaria, alba, by pollen of V. lychnitis, alba.
We tbus see, from the eight pure, cross, and hybrid unions of F. blattaria alba and lutea given in the above comparative table, that though the white variety exceeds in fertility the yellow variety, when both are fertilised by their own pollen, the yellow variety, inthe mixed unions, is in every case more highly fertile than the white. In the different unions of F. lychnitis, alba and lutea, there is some little discordance, this, however, is confined to the hybrid unions which are as yet very insufficiently illustrated, as may be seen by consulting Tables 3 and 4. In the case of the pure aud cross unions, we see, as in those of V. blattaria, that in the pure unions the white variety, and in the cross unions the yellow variety is the more fertile.
I know not whether this concordance is casual or otherwise, but I was so forcibly struck with it in the comparative study of my Tables, that I have thus ventured a special statement. I have been more especially induced to notice it also from its evidently bearing and illustrating, as I am inclined to think, that view of Mr. Darwin, (loc. cit.) respecting the good derived from cross fertilisation; inasmuch as we see that the yellow and original, or normally coloured, form of the species is less fertile than the white or derivative form in the pure unions, whereas in general, in the mixed unions, the yellow variety relatively exceeds the white in the degree of fertility. Any how, the mere fact of such variations occurring, whether or not they have any bearing on other points of theoretical natural science, seems to me worth noticing, as affording an additional link to that broken chain of
evidence which is said to disjoin the serial continuity of the phenomena of mongrelism and hybridism.
In Table 7 we have several unions of the yellow variety of V. thapsus. If we compare these results, we see that the fertility of the V. thapsus, lutea, by its cross-unions with the V. thapsus, alba, is decreased in the proportions of 94 relatively to 100, the product of fertilisation by its own pollen. We also see a great difference in the degrees of potency of the two pollens of the white and yellow variety of V. lychnitis on the stigmas of the yellow variety of V. thajisue; the pollen of V. lycltnitis, alba, exceeding in its fertilising influence that of V. lychnitis, lutea, in the proportion of 54 : 46. Judging from the results of the seven hybrid unions given in this Table, we also see how little the recognised systematic allinities of species guide us in pronouncing a priori as to the degree of fertility of their several unions. For example V. thupsijorme, V, virgatum and V. blaUaria, though much more closely allied to the V. thapsits 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, alia, 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. phaniceum, 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 eases as the present, in which the ovaries