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Show 26 INTRODUCTORY REMARKS. CHAP. I. . Another table exhibits the striking results spec1es. 1 t" from fertilising plants, which during severa genera Ions had either been self-fertilised or had been c~ossed with plants kept all the time under closely s~~llar d .t. 'th pollen taken from plants of a distinct con 1 Ions, w1 . stock and which had been exposed to dl:fferont con-d .t. I the concluding chapters vanous related l lOllS. n ·11 b points and questions of general interest Wl o discussed. . Anyone not specially interested i~ the subJect need not attempt to read all the deta1ls; though they possess, I think, some value, and cannot be all summarised. But I would suggest to the reader to t ake as an example the experiments on Ipom~~ in_ Cha~ter II.; to which may be added those on D1g1~ahs, Onganum Viola or the common cabbage, as 1n all these case~ the 'crossed plants are superior .to th~ selffertilised in a marked degree, but not 1n qu1te the same manner. As instances of self-fertilised plants being equal or superior to the crossed, the experiments on Bartonia, Canna, and the common pea ought to be read; but in the last case, and probably in that of Canna, the ' want of any superiority in the crossed .plants can be explained. Species were selected for experiment belonging. to widely distinct families, inhabiting various countnes. In some few cases several genera belonging to the same family were tried, and ihese are grouped together · but the families themselves have been arranged not 'i n any natural order, but in that which was the most convenient for my purpose. rrhe experiments have been fully given, as the results appear to me of sufficient value to justify the details. Plants bearing hermaphrodite floweTs can be interbred more closely than is possible with bisexual animals, and are there· CHAP. I. INTUODUCTORY REMAHKS. 27 fore well-fitted to throw light on the nature and extent o~ the g~od. effects of crossing, and on the evil effects ?f close Interbree~ing or self-fertilisation. The most ·1 Important conclusion at which I have arrived is that tho mere act of crossing by itself does no good. The g?od . depe~ds on the in eli vid uals which are crossed ~Iff~n~g sh~htly in con~titution, owing to their prog. enltois ha:Ing bee~ subJected during several generations. to slightly different conditions, or to what we call In. our ignorance spontaneous variation. This conclusio~, as ~e s~all hereafter see, is closely connected with vanous Im_PoTtant physiological pToblems, such. a_s the be~e:fit denved from slight changes in the cond_Itlons of hfe, and this stands in the closest connection with life itself. It throws light on the origin of the two sexes and on their separation or union in the same. i~dividual, and lastly on the whole subject of hybndism, which is one of the greatest obstacles to the general acceptance and progress of the great principle of evolution. In oTde1· to avoid misapprehension, I beg leave to repea_t that thToughout this volume a crossed plant, I ~eedhng, or. seed, means one of crossed parentage} that IS, one d.er~ved from a flower fertilised with pollen from a di~t_rnct plant of the same species. A.nd that a self-fertilised plant, seedling, or seed means one of self-fertilised parentage, that is, one derived from a flowe1· fertilised with pollen from the same flower or sometimes, when thus stated, from another flowe; on the same plant. |
