46 INBEEEDING AND OUTBREEDING 



Again, in the dioecious moss, Funaria, the Marchals;^^" 

 by a remarkable series of regeneration experiments, have 

 proven the determination of sex at the reduction division. 

 Each spore was found to contain the potentialities of but 

 one sex, but in the sporophyte they demonstrated the po- 

 tentialities of both sexes by inducing direct aposporous 

 development of gametophytes, which proved to have both 

 antheridia and archegonia, the organs of both sexes. 



The situation in hermaphroditic plants and animals 

 is not so clear. Particularly in plants the peculiar life 

 history with the introduction of alternation of generations, 

 makes, experimental work exceedingly difficult. Further- 

 more, there are many species of animals where the sex 

 ratio is nowhere near equality and where both external 

 and internal conditions undoubtedly do have marked in- 

 fluence, but in such a fundamental phenomenon we can 

 hardly believe these difficulties are insurmountable or 

 will lead to any radically different interpretation of the 

 problem. Where there is such clear cAridence from very dif- 

 ferent modes of attack and upon species so unrelated one 

 is constrained to believe the obstacles to a unified theory 

 are only superficial. This is particularly true since there 

 is another line of experimental evidence in favor of the 

 determination of sex by the chromosomes. Our whole 

 evidence on inheritance, in fact, is linked up with chromo- 

 some distribution, so that the easiest way to visualize the 

 process is by supposing that the individual potentialities, 

 the factors, which cooperate in the development of plant 

 and animal characters, are disposed in a definite manner 

 in the chromosomes, as we shall see in the next chapter. 

 The particular discoveries which demand our attention in 

 connection with the phenomenon of sex, however, are 



