358 BOTANICAL GAZETTE [NOVEMBER 



it seems to me more probable that the female is a neutral homozy- 

 gote (FF), the male having the formula FM, and the hermaphro- 

 dite the formula FMn> The gradually increasing number of known 

 instances of " spurious allelomorphism " proves that the pairing 

 of unlike or unequal genes in the heterozygote is, if not the general 

 condition, at least a not uncommon one. 



The question whether the sex genes are paired or unpaired in the 

 heterozygote, and if unpaired, whether the female is a positive or a 

 negative homozygote, might be settled by simple observation, if it 

 could be known that the chromosomes are the sex determiners, 

 as a number of recent cytological studies clearly suggest. It is 

 not at all certain, however, whether the unequal chromosome 

 groups in the male-producing and female-producing germ cells are 

 active determiners or simply passive indicators of other more 

 fundamental differences. The latter possibility is strongly empha- 

 sized by MORGAN (20), who shows that the pole to which the 

 accessory chromosome in Phylloxera is to proceed, is already deter- 

 mined before that chromosome has given any indication, by its 

 own motion, to which pole it will go. This suggests that the poles 

 of the dividing spermacyte may be sexually differentiated in ad- 

 vance by some other factor. If the chromosomes are not the sex- 

 determiners, but only passive indicators, the fact that they are 

 paired or unpaired, equal or unequal, has no decisive bearing upon 

 the question whether the female is a positive, neutral, or negative 

 homozygote, or whether the genes are paired or unpaired in the 

 heterozygote, for it is quite as easy to assume that the movement 

 of the accessory chromosome or "X-element" to the female pole 

 takes place in response to a tension caused by the absence of a 

 positive male sex-determiner at that pole, as that it is attracted 

 by the presence of a positive female determiner. If the " X-element " 

 should move into the vacancy caused by the absence of the sex- 

 determiner, the presence of the added chromosome or group of 

 chromosomes would become the evidence of the absence of the 

 sex gene; in other words, the female possessing the added chromo- 

 some would be a negative homozygote. All this is highly specula- 

 tive, and as there appears to be no way as yet to put the matter 

 to experimental test, it seems futile to discuss further the question 



