On the mode of Inheritance of certain Characters etc. 305 
(7) That in the eversporting forme the X chromosome which 
disappears from the pollen mother cell is always the one which 
carries S. (This is necessary on the theory that pollen capable of 
functioning must contain an X chromosome since experiment shows 
that here all such pollen grains carry s i. e. doubleness). 
(8) That in the pure-breeding singles there is no need to suppose 
that the disappearing X chromosome of the male gametes is any 
particular one. Since here every X chromosome may be supposed to 
carry S it makes no difference which of the pair is lost. It is this 
character which constitutes the difference between the pure-breeding 
and the eversporting types. 
(9) That the inheritance of plastid colour can similarly be ex- 
plained on the assumption that W (= white plastids) like S is located 
in the disappearing X chromosome in the sulphur-white strain — 
a strain which is eversporting in regard to plastid colour as well as 
singleness and doubleness and in which the pollen is found a// to 
carry creamness, although of the ovules, some carry whiteness and 
some creamness. Whereas in pure-breeding whites W need not be 
supposed to be located in this particular chromosome, since here 
every X chromosome will carry W. 
The above is a brief outline of only the main points of GoLD- 
SCHMIDT’s scheme, but contains, I think, all the matter essential to 
the present discussion. To have given further detail would have 
necessitated practically a recapitulation of the whole paper, which I 
have therefore not attempted. We may now consider these various 
assumptions in relation to the facts. 
With regard to the general conclusions contained in (I), (2) and 
(3) GoLDSCHMIDT himself admits that he can bring forward no evi- 
dence in support of the occurrence of this X chromosome in plants. 
He is obliged, therefore, to presume the existence of some invisible 
cell constituent which functions in plants in the same way as this 
X chromosome in those animals in which it has been found to occur. 
This conception of the existence of an X substance in plants, 
functioning like the X chromosome found in certain animals, forms 
the foundation upon which GOLDSCHMIDT constructs his whole scheme 
of interpretation of the facts regarding the inheritance of doubleness 
and plastid colour in Stocks. As however this assumption is not 
supported by any evidence, nor, so far as appears, can it be put to 
the proof, it can claim nothing in its favour in these respects as 
against the view which I have suggested. 
