47 



Laurent (1903) lias maintaiued that an excess of nitrogen or lime 

 favors tlie development of males in spinach, hemp, etc., while potash and 

 phosphoric acid favor the devo1o])ment of females, but his results are not 

 very convincing. Temi)erature, light and moisture conditions, relative age 

 and vigor of parents, I'elative maturity of pollen, early and late planting, 

 pruning, etc.. Iiave all been carefully and elaborately tested without achiev- 

 ing satisfactory or convincing results. The case of the anther smut cited in 

 the foregoing seems to furnish tlie best evidence among plants that the sex 

 of the spores to be developed can be changed by environmental conditions, 

 yet it must be admitted that the jjreponderance of evidence is against the 

 view that environmental conditions, either direct or indirect, can determine 

 sex. On the other hand, there are many who believe that sex is predeter- 

 mined in the germ <.'ells, and that we are confronted with a probleui which 

 is purely hereditary. According to this view certain parts of the hereditary 

 substance or chromatin contain male characters, or repesent maleness only 

 and certain other parts female characters, or femaleness, that is, there are 

 male determinants and female determinants in the chromatin. To illustrate 

 this statement, let us recall the case of the common liverwort, Marchantia. 

 Of the spores produced by any individual sporophyte, some will give rise 

 only to male thalli and others to female thalli irrespective of environmental 

 conditions. Now. the spores producing only male plants must contain only 

 male determinants, or male determining parts of the chromatin must domi- 

 nate over the female determinating parts in those spores and vice versa. 

 If the determination of sex be regarded as a problem of heredity, and if 

 we believe that hereditary jihonomena have a physical basis, some such 

 theory as the foregoing certaiidy affords a rational basis for further investi- 

 gation. 



