ALLEN— SEX INHERITANCE IN SPH^ROCARPOS. 313 



cytoplasmic ratio ; and which determine in the one case the consid- 

 erable but relatively slightly specialized development of the egg, and 

 in the other the remarkable metamorphosis of the androcyte into the 

 antherozoid. This is but a partial analysis of the nature of the 

 processes whose causes are to be explained, but it is sufficient to 

 illustrate the nature and complexity of the problem. 



Perhaps it is not safe to say more at present than that the ap- 

 pearance of the sex characters falling within the form-structure 

 category are to be ascribed to factors which in some way are de- 

 pendent upon, carried by, or inherent in, the X- and Y-chromosomes 

 — the word " factor " here being used in its ordinary, not in a tech- 

 nical Mendelian sense. Nothing in our present knowledge of the 

 mechanism of inheritance in Sphccrocarpos would justify us in hold- 

 ing that the factors here in question are of the nature of those which 

 are postulated by any particular theory of heredity. The conclu- 

 sion, if it can be so called, to which we are for the present led, is 

 therefore that one category of sex characters is reasonably explain- 

 able by the difference in mass between the sex chromosomes ; and 

 that those of a second category seem to result from some other, but 

 unknown, specific peculiarities of the same chromosomes. 



On the analogy of the irregularities which, it seems well estab- 

 lished, occur, though rarely, in the distribution of the sex chromo- 

 somes during the reduction divisions in certain animals, it is perhaps 

 to be expected that irregularities more or less like these will be 

 found in Sphccrocarpos. The occurrence of " non-disjunction," for 

 example, m.ight lead to the formation of a tetrad two of whose 

 spores have both an X- and a Y-chromosome each, the other two 

 spores possessing neither. It would be idle to speculate as to the 

 effect of such a distribution upon the viability of the spores or upon 

 the sexuality or sterility of the resulting plants ; but it is plain that 

 the result might well be a disturbance of the normal 2 : 2 sex ratio. 



Other irregularities than non-disjunction might conceivably like- 

 wise lead to modifications of this ratio ; and so it will not be surpris- 

 ing should a study of the results of the germination of large numbers 

 of spores bring to light occasional exceptions to the general rule of 

 the distribution of sex characters. It is possible that some of the 



