312 PLANT HYBRIDIZATION BEFORE MENDEL 



constant characters which appear in the several varieties of a group of 

 plants, may be obtained in all the associations which are possible accord- 

 ing to the mathematical laws of combination, by means of repeated arti- 

 ficial fertilization!' (p. 355.) 



Mendel now undertook to draw conclusions from his data. As 



we have seen : 



"The offspring of the hybrids of each pair of differentiating charac- 

 ters 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- 

 fertilization in a hybrid, the resulting offspring form the terms of a 

 combination-series in which the combination series for each pair of dif- 

 ferentiating characters are united." (p. 356.) 



Mendel then comes finally to these fundamental conclusions : 



"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 fertil- 

 izing 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 fertilization of pure species. We must therefore regard it as cer- 

 tain 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 produced in one plant or even in one flower of a plant, the 

 conclusion appears logical that in the ovaries of the hybrid, 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 that 

 these egg and pollen cells agree in their internal composition with those 

 of the separate forms. Cp. 356.) 



"In point of fact it is possible to demonstrate theoretically that this 

 hypothesis would fully suffice to account for the development of the 

 hybrids in the separate generations, if we might at the same time assume 

 that the various kinds of egg and pollen cells were formed in the hy- 

 brids on the average in equal numbers!' (Italics inserted.) (p. 357.) 



It was necessary, however, to put these last conclusions to ex- 

 perimental proof. 



We have seen from Mendel's results, that in any Y^ generation 

 of a hybrid, the ratio of the "impure" or hybrid type to either 

 of the pure types is as 2:1. 



We have also seen that the whole of any Fo generation pro- 

 duced by self-fertilization of the originally formed hybrids of 

 the F^ generation, consisted of : 



25% + 50% + 25% 



pure impure pure 



dominants dominants recessives 



DD Dr rr 



i.e., 1S% 20c 



apparent D pure r 



