14 



relation of each pair of different char- 

 acters in hybrid union is independent 

 of the other differences in the two 

 origifial parental stocks. 



If n represents the number of the 

 differentiating characters in the two 

 original stocks, 3" gives the number of 

 terms of the combination series, 4" the 

 number of individuals which belong to 

 the series, and 2" the number of unions 

 which remain constant. The series 

 therefore contains, if the original 

 stocks differ in four characters, 3^ = 81 

 classes, 4"* = 256 individuals, and 2^ = 

 16 constant forms; or, which is the 

 same, among each 256 offspring of the 

 hybrids there are 8 1 different combina- 

 tions, 16 of which are constant. 



All constant combinations which in 

 Peas are possible by the combination 

 of the said seven differentiating char- 

 acters were actually obtained by re- 

 peated crossing. Their number is given 

 by 2'^ = 128. Thereby is simultane- 

 ously given the practical proof that 

 the constant characters which appear 

 if? the several varieties of a group of 

 plants may be obtained w all the asso- 

 ciatio?Js which are possible according 

 to the [mathematical] laws of com- 

 binatio?i, by means of repeated artifi- 

 cial fertilisation. 



As regards the flowering time of the 

 hybrids, the experiments are not yet 

 concluded. It can, however, already be 

 stated that the time stands almost ex- 

 actly between those of the seed and 

 pollen parents, and that the constitu- 

 tion of the hybrids with respect to this 

 character probably follows the rule 

 ascertained in the case of the other 

 characters. The forms which are se- 

 lected for experiments of this class 

 must have a difference of at least 

 twenty days from the middle flower- 

 ing period of one to that of the other; 

 furthermore, the seeds when sown 

 must all be placed at the same depth in 

 the earth, so that they may germinate 



MENDEL 



simultaneously. Also, during the whole 

 flowering period, the more important 

 variations in temperature must be 

 taken into account, and the partial 

 hastening or delaying of the flowering 

 which may result therefrom. It is clear 

 that this experiment presents many dif- 

 ficulties to be overcome and neces- 

 sitates great attention. 



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 rec- 

 ognition in the experimental plants, all 

 behave exactly alike in their hybrid 

 associations. The offspring of the hy- 

 brids of each pair of differentiating 

 characters are, one-half, hybrid again, 

 while the other half are constant in 

 equal proportions having the char- 

 acters of the seed and pollen parents 

 respectively. If several differentiating 

 characters are combined by cross-fer- 

 tilisation in a hybrid, the resulting off- 

 spring form the terms of a combination 

 series in which the combination series 

 for each pair of differentiating char- 

 acters are united. 



The uniformity of behaviour shown 

 by the whole ojF the characters sub- 

 mitted to experiment permits, and fully 

 justifies, the acceptance of the prin- 

 ciple 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 experiment 

 with peduncles of different lengths 

 gave on the whole a fairly satisfactorv^ 

 result, although the differentiation and 

 serial arrangement of the forms could 

 not be effected with that certainty 

 which is indispensable for correct ex- 

 periment. 



THE REPRODUCTIVE CELLS 

 OF THE HYBRIDS 



The results of the previously de- 

 scribed experiments led to further ex- 



