192 Plant Genetics 



There is an apparently easy experiment which should 

 test these claims and decide between them, but as yet 

 it has not been performed. Fern prothallia are known 

 at times to produce proliferations which reproduce the 

 parent prothallium vegetatively. If a proliferation 

 could be produced on the archegonium-bearing region of 

 a mature prothallium its sexual behavior should throw 

 much light upon this problem. According to the physio- 

 logical claim, this proliferation should first produce 

 antheridia, for it will pass through a young stage of low 

 nutritive capacity. According to the cytological claim 

 the cells from which the proliferation arose have female 

 potentialities only, and therefore the prohferation should 

 never produce antheridia but only archegonia. 



Seed plants. — Most of the work on sex determina- 

 tion has been carried on with seed plants. Experiments 

 have been performed to show the effect of manuring, 

 light, temperature, and other environmental factors 

 on the sex ratio. The results have been both positive 

 and negative. Some conclude that sex is rigidly pre- 

 determined in the seed, while others claim that it is 

 determined by the later environmental conditions. 

 The general results are not conclusive, so that they may 

 be passed by with this brief statement. 



There are certain theories of sex determination, 

 however, with which every botanist should be familiar, 

 for they are an important part of botanical literature. 

 They may be stated briefly. 



CoRRENS (4) thought that sex was determined at the 

 reduction division of the pollen mother-cell. Two pol- 

 len grains are produced having female tendencies and 

 two having male tendencies. The sex of the progeny, 



