On the mode of Inheritance of certain Characters etc. 307 
which the variation from the exact ratio is in the direction of a 
distinct deficiency of doubles to counterbalance those in which the 
variation is in the opposite direction? We do not meet with them 
{see above, p. 300 where the data on this point are discussed). This 
consideration alone, viz. that on GOLDSCHMIDT’s sex-theory scheme 
the expectation is a ratio of 1s:1d, whereas the facts undoubtedly 
indicate an unequal ratio, appears to me sufficient to show that 
this cannot be the true explanation. His alternative suggestion can 
scarcely be regarded as an explanation, it amounts practically to an 
admission that the theory does not work; for it says, in effect, that 
if the facts do not fit the theory then some unknown cause must 
be at work which somehow produces a constant deviation from the 
results which we ought on this theory to find. But if the theory 
cannot be framed to fit the facts, what, one is constrained to ask, is 
its value? 
Why should we go out of our way to assume that perhaps half 
the pollen is incapable of functioning when to all appearance the 
grains are all equally good? Or that two sister cells in every tetrad 
fail to develop, in the absence of any evidence that such is the case? 
Is it not pushing argument from analogy rather far to assume, 
because it has been suggested that the occurrence of hermaphrodites 
in certain normally bisexual animals and the facts of sex inheritance 
appear to be accounted for by the fact that the so-called X chro- 
mosome is present in some of the gametes and not in others, that 
therefore in a plant normally hermaphrodite, in which the distri- 
bution of certain characters is not the same for the male and female 
germs, an X chromosome must be supposed to exist in certain of the 
germs but not in others, and that these others come to nothing? And 
further, that if this chromosome cannot be found, some hypothetical 
cell constituent must be supposed to be present which functions in 
the same way, i. e. to say which has localised in it the factors deter- 
mining any character showing sex-limited inheritance? 
But let us consider another discrepancy between GOLDSCHMIDT’S 
theory and the facts which is of fundamental importance. GOLD- 
‘SCHMIDT extends his theory to cover the case of the inheritance of 
plastid colour. He holds that the facts can be explained if we locate 
yet another factor in the hypothetical X chromosome equivalent viz. 
W, the factor which gives white (—colourless) plastids. (On my view, 
on the other hand, the inheritance of plastid colour furnishes one 
more example of the type of partial coupling which sufficed to 
