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instance the homochromatic unions with yellow as female exceed in fertility the converse heterochromatic union; but in the other cases given in lines 3 and 5, this higher fertility of the homochromatic unions is yielded by the white variety; the relative proportions of those being much more marked than in the above cases of the heterochromatic union with the yellow variety as female, viz., as 4 to 3, whereas, as we have seen, in the heterochromatic, A. 1, the proportions are as 7 to 6. In further illustrations of this point we see in B. 2 that the yellow homochromatic union of V. lyclmitis, lutea, by pollen of V. thapsus, lutea, relatively to the heterochromatic unions of the former with pollen of V. thapsus, alba, is nearly as 5 to 4, so that we here again see (as in the heterochromatic and homochromatic unions in A 1) a more intimate approximation between the products of these two anions, than occurs in the other cognate unions of B. 2, in which the white variety is the more fertile.
These curious relations, however, as I have already shown, are partly explained by the fact,—though we can only dimly see why it should be so,—that in the pure unions of the white and yellow varieties of the above mentioned species, the white, in every case, yields more seed than the yellow; whereas in the cross-unions the yellow variety in general is the more productive. But, it may be asked, how is the greater potency of the pollen of the white variety relatively to that of the yellow variety, as shown in the above tables to be accounted for? Does it really imply thnt the female element of the yellow variety yet retains its normal or original potency, the male element alone having become absolutely less potent, as compared with the male element of the white variety. This hypothesis, analogically considered, does not seem to me at all improbable. I think we have clearly seen by the comparative results of the pure* and mixed unions of the yellow variety with those of the white, that the pure unions of the yellow do not yield a degree of fertility at all proportionate to that of the like unions of the white variety, as judged by the relative fertility of their cross-unions; and that accordingly this would seem to be due to an acquired weakness in the generative powers of the yellow variety. In noticing this point in a former part of my paper, I treated it as if both sexual elements had undergone a similar decrease in their generative powers; but we here see that it is more particularly, if not altogether confined to the male element. Now, as the results of hybridisation show that the pollen is more susceptible to the concomitant sterilising action of hybridism than the female element, may wc not suppose that the debilitating effect of continued self-impregnation will also manifest itself more quickly in the male than in the female element, and thus afford an explanation of the decreased sexual powers of the male, as compared with the female element, in the yellow varieties of the above species of Verbasca furthermore, showing us that as it has been a slowly acquired quality, so will it be in its elimination and regainment of its pristine vigour.
The relations of the several reciprocal unions in the above tables is another point which we must briefly consider, as having most important bearings on the subject of our present enquiry. A hasty examination suffices to show that these are much complicated. Thus V. lychinitis, luted, in its two unions with the white and yellow varieties of V. llattaria, the heterochromatic unions are the more fertile; whereas in its two unions with the white and yellow varieties of V. thapsus, we find it yields the more fertile by a homochromatic union. Again V. llattaria, lutea, in its four distinct unions with the white and yellow varieties of V. thap>ws and V. lychnitis, yields the higher degree of fertility in the heterochromatic unions, while the V. llattaria in its similar unions with the white and yellow varieties of V. thap>sus and lychnitis is, singularly enough, more highly fertile in the homochromatic than the heterochromatic unions. Lastly the V. thapms, lutea, yields more seed by its heterochromatic unions with pollen of the V. lychnitis, alia, than by its homochromatic unions with the V. lychnitis, lutea; whereas in the converse unions we have seen that the V. lychnitis, lutea, is more fertile in the homochromatic unions with V. thapsus, lutea, than in the heterochromatic unions with V. thapsus, alia I
The tabulated experiments given in C. 3, afford another source of complexity to the question under examination, inasmuch as they are quite irregular in the relative degree of fertility produced by the affinity of colour. Thus by the three unions of V. lychnitis, lutea, with pollen of the three varieties of V. phceniccum, the most highly fertile is that in which V. lychnitis, lutea, is treated with pollen of the purplish violet, or normal form, the average in this being 25 seeds per capsule; then follows the unions with[ pollen of the white variety, the average of seeds being in these 21 seeds per capsule ; and lastly in the unions with the variety with rosecoloured flowers, the fertility of V. lychnitis, lutea, is reduced to the low average of 18 seeds per capsule. Thus judging by the degrees of fertility, we clearly see that the natural functional co-relations of these plants in place of being regulated by their respective colour affinities, arrange themselves in an entirely independent and opposite scale ; the extremes in the scale of colour given, viz., the purplishviolet with yellow, manifesting the nearest functional co-relation. ^gain as a further complication we find that the white and yellow unions, —the most closely allied of the colours mentioned,—hold a medial position between the purplish violet and rose. How obviously futile then, we may well remark, would our d priori conclusions have been, as to the degrees of fertility of the above unions, on a presumed coordination between colour and function in the phenomena of hybridism 1
It would thus appear from the results given in the foregoing tables that in the hybridisation of varieties of distinct species characterised by differences of colour alone, no definite relations whatever can bo observed between the affinities of colour, and the degrees of fertility, but that in these cases as in the reciprocal hybridisation of pure species, the relative fecundity is a most variable and unpredicable quantum. This view seems to me to be further supported by the results of my experiments on the reciprocal hybridisation of the dimorphic species of Primulae* in which I showed that the laws of dimorphism were limited in their action to the unions of the two forms of a species ; the heteromorphic and homomorphic unions of distinct species proving irregularly the more fertile. From considering the important functional co-relations of the two forms of dimorphic species, and their trifling morphological characteristies, together with the specifically limited extent of their operations, we have less reason to be surprised, if a similarly limited relationship should ultimately prove to regulate the degree of fertility of those unions of differently coloured varieties of a species as in Verbascum and analogous cases. Indeed, judging * Linn. Soc. Jour. Vol. 8, p. 78.
from my previons remarks on the co-relations between the degree of fertility and affinity of colour in the crossing of varieties of a species, together with the results of the hybridising differently coloured varieties of distinct species, this law seems clearly indicated, that the relative degree of fertility of the cross unions between the differently coloured varieties of certain species is inversely proportionate to the les-; or more mediate colour affinities of these unions. Further that this law does not extend to, or regulate the hybrid unions of differently coloured varieties of distinct species, but is strictly limited in its operations to those unions of varieties of a single species. Such at least is the conclusion which my own experiments would indnce me to hold, but seeing that they are so directly opposed to the results of Gartner's large experience, I would rather avoid at present any* thing like definite or positive conclusions, until subsequent experiment affords us a crucial array of data.
In conclusion, I will now by a cursory retrospect of the above details, re-state a few of the more important points, which elucidate the mooted relations between the phenomena of the hybridisation of a species and the mongrolisui of the varieties of a species. First then in hybndism we see on the calculation of V. lychnilis yielding with its own pollen 100 seeds, it yields upon fertilisation with pollen of V. nigrum 80 seeds, by the pollen of V. virgatum 58 seeds, by that of V. phamiceum 66 seeds and by that of V. thapsifonne 46 seeds. In the unions of varieties of a species, with these of other species we find differences in the sexual powers, so that the pollen of the one variety of a species is less potent than that of the other on the stigmas of the same variety of another species. Thus V. lychnitis fertilised by the pollen of V. blattaria, lutea, yields 61 seeds, by that of V. blattaria, alba, 56 seeds, and again by pollen of V. thapsus, lutea, V. lychnitis yields 46 seeds, by that of V. thapsus, alba, 39 seeds, relatively in each case to the 100 seeds produced by its own pollen. Again we have evidence also of reciprocal differentiation in the relative sexual powers of varieties of a species, and those of other species. Thus in the case mentioned above of V. blattaria, the pollen of variety alba is more potent on the stigma of V. lychnitis than that of variety lutea, whereas in the converse unions of these forms, we find that the pollen of V. lychnitis is more potent on the stigmas of V. blattaria, lutea, than that on those of the variety alba, in the proportion of 40 to 26.
Secondly, in mongrelism, we also find variabilities in tho relative sexual powers of varieties of a species, by differences in the degrees of fertility resulting from their simple and reciprocal unions. Thus on the calculation of V. phceniceum, yielding 100 seeds by fertilisation by its own pollen, it yields with that of the variety rosea 68 seeds, and by that of the variety alba, 56 seeds, or nearly as 5 to 3. In the reciprocal unions of these varieties, we also find variabilities in their converse sexual powers. For example, in the reciprocal unions of V. phceniceum and varieties, the potency of the pollen of rosea relatively to that of alba on the stigmas of the normal form is nearly as 5 to 4 ; whereas the pollen of the latter on the stigmas of rosea and all>a is as 4 to 3. This difference in the reciprocal sexual powers of varieties when crossed is so regulated however by colour affinities, that unlike the irregular and indefinite results of the reciprocal unions of varieties of distinct species, judging by my own experience, we see that the pollen of rosea is more potent on the stigmas of the normal form than these of alba and so conversely, the pollen of the normal form is more potent on the stigmas of rosea than on those of alba. In those cases, however, in which colour differences do not come into play the pollen of one variety, relatively to that of another variety of the same species is so differentiated with respect to their reciprocal stigmatic relations that the grade of fertility of the pure unions of these varieties does not at all correspond with that of the cross unions. For example, in the pure unions of varieties lutea nnd alba of V. blattaria, the fertility of the latter exceeds that of tho former in about the proportions of 12 to 11 ; whereas in their converse unions, lutea exceeds alba in the higher proportions of 6 to 5 I Thus in the inter-crossing of varieties of a species, as in the inter-crossing of varieties of distinct species, there are converse variabilities in the reciprocal sexual powers of their respective elements.
As the facts stand then, it appears to mo that in the first crosses of the varieties of certain species, as in the first hybrid crosses of distinct species, a variable degree of sterilisation results, and again, that tho relative sterilising inlluence is as highly intensified in tho crossing of undoubted varieties of certain species, as it is in the hybridising of