336 EVOLUTION AND GENETICS 



sex-cords from the peritoneum enter the ovary in the fowl, and 

 that the absence of growing oocytes permits the development of 

 these cords into male structures. For a detailed consideration 

 of sex reversal Crew's paper should be consulted. 



Schaffner's Plants. The conclusive results obtained by Schaff- 

 ner in his experiments on the determination of sex in plants must 

 be regarded as among the greatest contributions since the discovery 

 of the sex chromosomes. These experiments have been conducted 



Fig. 190. — A Buff Orpington hen tliat became a cock. Two stages early 

 and late, in the reversal of sex. This hen laid eggs from which normal chicks 

 were hatched, and later became the father of normal chicks. (From Shull's 

 Heredity. McGraw-Hill Book Company, Inc., by permission.) 



chiefly on hemp (Cannabis saliva L.), but corn and various other 

 plants have also been used. Plants have been reared under various 

 conditions of environment and the results show that it is possible 

 to determine the sex of the individual at will by changing the 

 food supply, or to bring about reversal in a plant which has 

 previously developed an inflorescence of one or the other sex. 



One of the most striking of Schaffner's experiments was the 

 production of Siamese twins of opposite sex in the jack-in-the- 

 pulpit (Arisaema triphyllum L.). The result was obtained by 

 very careful control of the food supply of the two individuals. 

 Since the plants developed from a forked corm the control could 

 not be accomplished through quantitative treatment but only 

 through artificial reduction of the leaf surface of one plant and 

 such other factors as might influence its capacity for photosjm- 

 thesis and food storage. In spite of the fact that Arisaema twins 

 are normally of the same sex or shnilarly monoecious, the result 



