THE CACTUS 163 



spineless cactus, on the other hand, retains the 

 factors for spines in its germ plasm, to make 

 their influence tangibly felt in a large propor- 

 tion of the offspring. 



Nevertheless, it does not appear that the con- 

 dition of spininess acts as a simple Mendelian 

 dominant. On the contrary, it appears that the 

 hereditary conditions that govern the spiny con- 

 dition in the cactus are very complex. The best 

 interpretation would seem to be that there are 

 multitudes of factors for spicules and spines, 

 variously blended in the germ plasm of any given 

 individual. The spiny condition, on the whole, 

 tends to be dominant to the spineless condition, 

 because the spines are a relatively late develop- 

 ment in the history of the evolution of the cac- 

 tus tribe. 



But doubtless the period in question was an 

 exceedingly long one, covering many thousands 

 of cactus generations, during which the plants 

 were becoming better and better protected; and 

 each stage of such development may be thought 

 of as having its hereditary factors in the germ 

 plasm, capable of acting independently. 



Thus it is that in the same fraternity some seed- 

 lings are exceedingly spiny, while others have 

 a comparatively small number of spines, and a 

 few may be absolutely spineless. Thus, also, is 



