MENDEL'S LAW 13 



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

 important starting-point is furnished by the pea in the 

 fact that, among the descendants of the hybrids, 

 constant forms appear, and these in all combinations of 

 the mated characters. According to experience, we find 

 it everywhere the rule that constant descendants can be 

 produced only when the egg cells and the fertilizing 

 pollen are of like kinds : that is when both are furnished 

 with the materials * to produce individuals completely 

 alike, as happens in the normal fertilization of pure 

 kinds. We are therefore forced to the conclusion that, 

 in the production of constant forms among the hybrids, 

 completely similar factors co-operate. Since the various 

 constant forms are produced not only on a single plant, 

 but even in a single flower of that plant, the conclusion 

 seems sound that, in the ovaries of the hybrids as many 

 kinds of egg cells and in the anthers as many kinds of 

 pollen cells are formed as there are constant combina- 

 tion forms possible ; and these egg and pollen cells 

 correspond in their inherent constitution j^ with the 

 separate forms. Indeed it could be shown theoretically 

 that this hypothesis would explain completely the 

 behaviour of the hybrids in the different generations if 

 it could be granted at the same time that the various 

 kinds of egg and pollen cells are formed in the hybrids 

 in equal numbers on the average." 



Mendel's statement may be simplified by being 

 resolved into the following four propositions, the first 

 three of which are mere statements of fact with deduc- 

 tions which are obvious, while, in the last, the law he 

 was in search of is inferred : 



* Anluge. f Ihrcr innern Beschaffenheit nach. 



