S3^ THE GERM-PLASM 



that in the United States of America nine mules out of every 

 ten are striped. 



Before concluding this section, I will analyse a case of 

 reversion to remote ancestors in plants in greater detail. Mv 

 reason for so doing is not because different principles are 

 necessary for its explanation, but because we possess the results 

 of experiments which render a closer examination of the theory 

 possible. 



I will select as an example the case of the reversion of 

 irregular or unsy7n}jietrical flowers to a regular or peloric form. 

 Many instances of reversion of this kind have been described, 

 but they are very exceptional : their origin cannot be connected 

 with any external causes, and must evidently be due to purely 

 internal ones, viz., to the composition of the germ-plasm. 



If my opinion concerning the transformation of the germ- 

 plasm in the course of phylogeny is correct, it follows, as has 

 already been shown, that individual unmodified determinants of 

 an old character must always appear here and there in the 

 germ-plasms of the modern species, even after an enormous 

 number of generations. Such ancestral determinants — those 

 of the original regular flowers, for instance — need not by any 

 means be contained in the germ-plasm of every individual 

 plant ; and the older the modern species is, the fewer will be 

 the number of these determinants, wiiich we will call ' peloric.' 

 They must gradually be displaced by the ' asymmetrical ' deter- 

 minants ; for the latter, being better adapted to the existing 

 conditions, have a better chance in the struggle for existence. 

 A large number of plants, such as Corydalis tuber osa, for 

 instance, will thus no longer contain any ' peloric ' determinants, 

 and this makes it apparent why reversion so seldom occurs in 

 these cases. The fact that it can occur at all, is to be accounted 

 for by the processes of reducing division and amphimixis in two 

 germ-cells, the latter of which always follows on after the 

 former. For if a small number of ' peloric ' determinants still 

 remained in various idants of individual plants of the species in 

 question, they might occasionally come together in one germ- 

 cell owing to the reducing division ; and if two such germ-cells 

 meet one another in the process of fertilisation, this group of 

 determinants may predominate, and reversion will then occur 

 — provided that the combined power of these ' peloric " deter- 



