ALLEN— SEX INHERITANCE IN SPH^ROCARPOS. 309 



course of the divisions which formed the spores. The invariable 

 connection of the X-chromosome with femaleness and of the 

 Y-chromosome with maleness seems to prove a causal relation of 

 some sort between the presence of either chromosome and the ap- 

 pearance of the characters of the corresponding sex. The further 

 logical step seems likewise inevitable, although admittedly it raises 

 questions of considerable difficulty — the conclusion, namely, that it 

 is the presence of an X- or of a Y-chromosome in the cells of a 

 particular plant which determines the appearance in that plant of 

 the characters of the corresponding sex. This essentially corre- 

 sponds with the hypothesis which the students of the sex chromo- 

 somes of animals seem in general to have adopted — although natu- 

 rally the form of the statement, as of the precise fact, is different 

 for an organism whose sexual generation is diploid rather than 

 haploid. 



The facts in the life of Sphcvrocarpos that seem to force this con- 

 clusion upon us are, first, that, as already noted, the physical bases 

 for the sex characters must have been separated in the course of 

 the divisions in the spore mother cell and distributed among the 

 four resultant spores ; and second, that the only structures that are 

 shown to have been so separated and distributed are the X- and 

 Y-chromosomes — the four spores being to all appearances alike in all 

 other points of structure, form, and size. The difficulty of imagin- 

 ing how the sex chromosomes can function in impressing sex char- 

 acters upon the plant — a difficulty which, however, is but of the 

 same order as that which confronts the very widely accepted theory 

 of the function of the chromosomes in inheritance in general — will 

 continue to breed a healthy skepticism and will stimulate the attempt 

 to find another basis for sex inheritance ; but at present this hypothe- 

 sis of the significance of the sex chromosomes seems the only intel- 

 ligible one and the one therefore upon which further investigations 

 must rest. 



The question then arises as to how the sex chromosomes of 

 Sphcvrocarpos can be conceived as exercising their controlling influ- 

 ence. Apparently this question may be answered in different ways 

 as regards the two categories of sex characters already mentioned. 



The notion suggests itself at once that the differences in size and 



