332 APPENDIX 



If we endeavour to collate in a brief form the results arrived at, 

 we find that those differentiating characters, which admit of easy 

 and certain recognition in the experimental plants, all behave 

 exactly alike in their hybrid associations. The offspring of the 

 hybrids of each pair of differentiating characters are, one-half, 

 hybrid again, while the other half are constant in equal proportions 

 having the characters of the seed and pollen parents respectively. 

 If several differentiating characters are combined by cross-fertili- 

 sation in a hybrid, the resulting offspring form the terms of a com- 

 bination series in which the combination series for each pair of 

 differentiating characters are united. 



The uniformity of behaviour shown by the whole of the char- 

 acters submitted to experiment permits, and fully justifies, the 

 acceptance of the principle that a similar relation exists in the other 

 characters which appear less sharply defined in plants, and there- 

 fore could not be included in the separate experiments. An experi- 

 ment with peduncles of different lengths gave on the whole a fairly 

 satisfactory result, although the differentiation and serial arrange- 

 ment of the forms could not be effected with that certainty which 

 is indispensable for correct experiment. 



The Reproductive Cells of the Hybrids 



The results of the previously described experiments led to further 

 experiments, the results of which appear fitted to afford some con- 

 clusions as regards the composition of the egg and pollen cells of 

 hybrids. An important clue is afforded in Pisum by the circum- 

 stance that among the progeny of the hybrids constant forms 

 appear, and that this occurs, too, in respect of all combinations of 

 the associated characters. So far as experience goes, we find it in 

 every case confirmed that constant progeny can only be formed 

 when the egg cells and the fertilising pollen are of like character, so 

 that both are provided with the material for creating quite similar 

 individuals, as is the case with the normal fertilisation of pure 

 species. We must therefore regard it as certain that exactly similar 

 factors must be at work also in the production of the constant forms 

 in the hybrid plants. Since the various constant forms are pro- 

 duced in one plant, or even in one flower of a plant, the conclusion 

 appears logical that in the ovaries of the hybrids there are formed 

 as many sorts of egg cells, and in the anthers as many sorts of 

 pollen cells, as there are possible constant combination forms, and 



