74 Indications of a Central Zone of Development 



descendant organism, to the definite function of develop-- 

 ment, and which differentiates itself gradually from the 

 other parts of this tissue by quite inappreciable and 

 gradual transitions. 



We have already said that the centroepigenetic 

 hypothesis makes it necessary to distinguish the effective 

 germinal zone, or true place of origin of the germinal 

 substance, from the apparent germinal zone, which would 

 be nothing else than the receiving station for the sub- 

 stance separated out or secreted by the effective germinal 

 zone, or the place where the sexual cells concerned are 

 built up out of this material. While we must regard only 

 the effective germinal zone as the central zone of develop- 

 ment, it is clear that the apparent germinal zone can be 

 located at any part whatever of the organism. 



In the higher plants the apparent germinal zone of the 

 asexual budding cells, and that of the female, sexual cells, 

 would seem generally to coincide approximately with the 

 actual zone, that is, with the corresponding central zone 

 of the leaf and of the flower. 



In this way can be explained the heretofore puzzling 

 phenomenon of the Xenia, in which as is known the 

 flower after a hybrid fecundation, often takes on the 

 form, size, color and tissue structure, characteristic of the 

 variety from which the pollen comes ; that is, as Darwin 

 has already observed "in which the male element not 

 only influences the germ as is its proper function, but 

 at the same time influences various parts of the mother 

 plant, in the same manner as it influences the same parts 

 in the seminal offspring from the same two parents." 4T 



47 Darwin : The Var. of Animals and Plants under Domestication. 

 Eighth impression of the second edition. Vol. I. London, Murray, 

 1882. Chap. XI, P. 433. 



