422 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



interpreted. Some have emphasized the fact that weak strains 

 do thus arise, which is interpreted as evidence that inbreeding 

 always results through its own influence in decreased vigor and 

 fertility (see discussion and conclusion of Kraemer, '14). The 

 very frequent cases of highly vigorous and fertile inbred strains 

 or of intensive line-bred strains (Wilsdorf, '12), however, compel 

 one to attribute the appearance of weakened inbred strains to 

 causes other than inbreeding itself. 



The results of experimental work with rats by King ('16) show 

 that inbreeding of pedigreed lines of albino rats for 22 generations 

 involving a total of io,ooo individuals has not led to any decrease 

 in constitutional vigor, but that there has been instead an increase 

 of body weight and fertility over that of stock albino rats. In 

 these experiments selectionifor size and fertility were quite second- 

 ary and incidental. Such results indicate that inbreeding is not 

 of itself to be considered as injurious. 



Relation of sterility from physiological incompatibility to vegetative 

 vigor and production of sex organs. — The physiological incom- 

 patibility involved in the sterility exhibited in chicory is quite 

 independent of any decrease in vegetative vigor, and it does 

 not involve in any degree the number of flowers produced. Al- 

 though the size of the plants and the relative number of flower 

 heads varied considerably, there is no correlation between the 

 number of flowers produced and the number of seed set either in 

 self- or in cross-sterility or fertility, and in all cases the actual 

 fertility bears no apjiarent relation to the potential fertility. It 

 was estimated that during the summer of 19 15 the self-sterile 

 plant A produced at least 1,000 flower heads, the self-sterile 

 plant C about 2,000, the self-fertile plant {E22 y. A) no. 10 about 

 2,200, and the various self-sterile plants of the red-leaved Treviso 

 variety about 2,500 each. Sister plants of the F3 generation were 

 most often quite alike in general vigor and habit of growth whether 

 self-sterile or self-fertile. Evidently it was such results as these, 

 together with the persistence of self-sterility even in plants neces- 

 sarily cross-bred, that led Darwin to the vague suggestion that 

 the causes of self-sterility of this type are sporadic and chiefly 

 environmental. 



The conditions in chicory in this respect are e\idently similar 

 to those reported for Eschscholtzia, Secalc, Cardamine, Nicotiana, 



