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Show 220 TIYBRIDIS:M. [CnP. VIII distinction between species and varieties; but. that the evidence from this source graduates away, and Is doubtful in the san1e degree as is the evidence derived from other constitutional and structural differences. In regard to the sterility of hybrids in successive generations; though Gartner was enabled to rear some hybrids, carefully guiding them from a cross with either pure parent, for six or seven, and in one case for ten generations, yet he asserts positively that their fertility never increased, but ·generally greatly decreased. I do not doubt that this is usually the case, and that the fertility often suddenly decreases in the :first few generations. Nevertheless I believe that in all these experiments the fertility has been diminished by an independent cause, namely, from close interbreedinO'. I have collected so large a body of facts, showing that close interbreeding lessens fertility, and, on the other hand, that an occasional cross with a distinct individual or variety increases fertility, that I cannot doubt the correctness of this almost universal belief amongst breeders. Hybrids are seldom raised by experimentalists in great numbers; and as the parent-species, or other allied hybrids, generally grow in the same garden,~ the visits of insects must be carefully prevented during the flowering season: hence hybrids will generally be fertilised during each generation by their own individual pollen ; and I am convinced that this would be injurious to their fertility, already lessened by their hybrid origin. I am strengthened in this conviction by a remarkable statement repeatedly made by Gartner, namely, that if even the less fertile hybrids be artificially fertilised with hybrid pollen of the same kind, their fertility, notwithstanding the frequent ill effects of manipulation, sometimes decidedly increa$es, and goes on increasing. Now, in artificial fertilisation pollen is as often taken by chance (as I know from my own experience) from the anthers of another flower, as from the anthers ot the flower itself which is to be fertilised ; so that a cross between t'vo flowers, though probably on the same plant, would be thus effected. Moreover, whenever complicated experiments are in progress, so careful an observer as CHAP VIII.] STERILITY. 221 Gartner would have castrated his hybrids, and this would have insured in each generation a cross with a pollen from a distinct flower~ either from the same plant or from another plant of the same hybrid nature. And thus, the strange fact of the incrense of fertility in the successive generations of artificially f ertilised hybrids may, I believe, be accounted for by close interbreeding having been avoided. Now let us turn to the results arrived at by the third most experienced hybridiser, na1nely, the Hon. and Rev. W. I-Ierbert. He is as emphatic in his conclusion that some hybri~s are perfectly fertile-as fertile as the pure parent species-as are Kolreuter and Gartner that some degree of sterility between distinct species is a universal law of nature. He experiinentised on some of the very same species as did Gartner. The difference in their results may, I think, be in part accounted for by I-Ierbert's g:eat horticultural s~ill, and .by his having hothouses at his command. Of his many Important statements I will here give only a single one as an example namely that " every ovuI e I. n a po d of 0 n.n um capense fe' rtilised b' y C. revolutu~ produced ~ plant, which (he says) I never saw to occur In a case of Its natural fecundation." So that we her~ ?av~ perfect, or even more than commonly perfect, fertility In a first cross between two distinct species. This case of the Crinum leads me to refer to a most si~gular f~ct, na~ely, that th~re are in~ividual plants, as With certain sp~mes of Lobeli~, and With all the species oft~~ genus Hippeastrum, whiCh can be far more easily fertlhsed by the pollen of another and distinct species than by th~ir own pollen. For these plants have bee~ found to :ywld s~ed t? the pollen of a distinct species, though quite ster1le With thmr own pollen notwithstanding .that tf!~ir o":n pollen w~s found to be perfectly good, for 1t fertilised distinct species. So that certain individual plants and all the individuals of certain species can actually ~e. hybridised.much more readily than they can be self-fertihsed! For Instance, a bulb of Hippeastrum auli- . cum pr?duced. four flowers ; three were fertilised by Herbert With their own pollen, and the fourth was subse- |