ALLEN— SEX INHERITANCE IN SPH^ROCARPOS. 299 



quite clear from these results that the general conclusion arrived at 

 by Douin and Strasburger for the species of Sphccrocarpos consid- 

 ered by them applies also to S. DonnelUi — namely, that the differ- 

 ences which distinguish female from male plants result from differ- 

 ences in the spores that are to give rise to them, and that of the 

 spores formed by the division of a single mother cell two bear fe- 

 male potentialities only and two male potentialities only. It seems 

 probable, too, that exceptions to this rule, if any occur, are less 

 frequent than might be thought from Douin's observations — his 

 apparently aberrant cases probably having resulted from some of 

 the causes of error already noted. It is not intended to be sug- 

 gested, however, that positive exceptions to the rule will not be 

 found. The possibility of such exceptions will be discussed on a 

 later page. The occurrence or non-occurrence of an exceptional 

 distribution of sex characteristics, and the proportion of such occur- 

 rences, if any, are evidently to be determined by the observation of 

 thousands of plants rather than of a few score. 



It will be noticed from Tables I. and II. that the number of 

 plants certainly referable to the respective sexes is substantially 

 equal: in the one case 30 females and 32 males, in the other 15 fe- 

 males and 14 males. Thus it appears that so far as power of germi- 

 nation is concerned there is no marked dift'erence between female- 

 producing and male-producing spores. This fact is striking in view 

 of the great difference in favor of the female plants in rate of 

 growth and in power of resistance to unfavorable conditions. Ap- 

 parently this difference, which for want of a better word may be 

 spoken of as one of "vigor," does not exist, or at least come to ex- 

 pression, as between the spores, but becomes apparent at some time 

 after germination and during the development of the gametophytes. 



While there seems to be no difference between the female- and 

 male-producing spores in their capacity for germination, it remains 

 possible that there is a difference in time or rate of germination. 

 On this question the foregoing observations throw no light, but a 

 suggestion is furnished by a recent set of experiments in which an 

 attempt has been made to study this particular point. On December 

 27 and 28, 1918, 67 tetrads from two capsules were sown in as many 

 pots of soil, one tetrad to a pot. Germination has been slow, and 



