44 



ture uor iiutritiou lias aiiythiiig to do with the determiuatioii of sex. He 

 asserts also that the three strains of Puuuett eau be found in one strain 

 and each is capable of producing the other types according as the data 

 is scanty or extensive. 



Even if we admit that the results obtained with certain animals furnish 

 some evidence in favor of the view that nutrition may be instrumental in 

 determining sex, yef the vast majority of facts obtained from numerous 

 studies made upon lower and higher plants point unmistakably to the 

 opposite conclusion. 1 shall mention a few instances. Botanists have long 

 recognized the difficulty of obtaiidng for class use the zygospores, or the 

 sexually formed reproductive bodies, in the common bread mould Rhizopus 

 nigricans, and this was supposed to be due to the lack of knowledge of the 

 external conditions necessary to call forth sexual reproduction. Blakeslee 

 has recently shown that this common mould is dioecious, and that if male 

 strains are cultivated along with female strains, sexual reproduction will 

 take place ii:respective of external conditions ; whereas if the different 

 strains are grown separately, no zygospores will result, no matter what the 

 food conditions may be Again, the well-known liverwort, Marchantia, 

 produces male and female sexual organs upon separate thalli, or individuals. 

 These individuals are propagated by bodies called gemmae, and it is re- 

 ported that Noll has cultivated individuals from the gemmae under all 

 sorts of growth conditions without being able to change the sex of any of 

 the thalli. The thalli arise primarily from spores that are apparently all 

 alike, and that come from the same capsule, yet some of these spores must 

 be strictly male and others female. The well-known studies of Prantl upon 

 fern prothallia are frequently quoted as supporting the doctrine that food 

 conditions determine sex. Prantl found that under poor conditions of nour- 

 ishment the prothallia produced only male organs, and if removed to con- 

 ditions affording good nourishment, female organs were developed. In 

 this as in many similar cases, there was no change of sex since monoecious 

 organisms Avere operated with, that is organisms capable of producing both 

 male and female gametes. Lack of nourishment merely inhibited the devel- 

 opment of the tissue upon which the female organs are borne, and con- 

 sequently only male organs were developed. These prothallia arise from 

 spores that contain the characters of both sexes, and external conditions 

 merely stimulate the development of one or the other of the sexes, or both. 



The writer has recently begun the study upon a fern, whose prothallia 

 liave been reported as strictly dioecious, and that if the spores are well 



