356 Mendel's Experiments 



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- 

 fertilisation in a hybrid, the resulting offspring form the 

 terms of a combination series in which the combination 

 series for each pair of differentiating characters are united. 

 The uniformity of behaviour shown by the whole of 

 the characters 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 therefore could not be in- 

 cluded in the separate experiments. An experiment with 

 peduncles of different lengths gave on the whole a fairly 

 satisfactory result, although the differentiation and serial 

 arrangement 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 conclusions as regards the composition 

 of the egg and pollen cells of hybrids. An important clue 

 is afforded in Pisum by the circumstance 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 



