FOR THE MENDELIAN LAws 659 
hybrids of the first generation organize germ cells which are of 
pure descent, and that these unite in fertilization according to the 
laws of chance. Taking a specific case by way of illustration, we 
can imagine the following to take place when the sex cells A(a) 
of say the second generation meet each other in fecundation. 
The pollen, which is of pure descent, unites with the egg, 
which also is of pure descent, and the chances of union may be 
thus expressed: 4a; AA; aa; aA. So that it happens, since 
the anther forms two sorts of germ cells and the ovary also two 
sorts, that in this way one half of the hybrids of say the third gen- 
eration will be of mixed descent, and one half of pure, the latter 
being equally recessive and dominant. The results as calculated by 
the laws of chance, are thus seen to be precisely the same as what 
is found empirically to occur. 
Such are the more essential facts and conclusions of the dis- 
covery by Mendel, and upon them are based the two so-called 
“laws”’ of Mendel, namely, the law of dominance and that of the 
splitting of the hybrid race. The latter alone concerns us at 
present. 
We now arrive at the interesting question, Is there a cytological 
basis for Mendel’s law of the splitting of the hybrid race ? 
Bateson has recently suggested the idea that the ‘essential 
part of the discovery (of Mendel—the italics are my own) is the 
evidence that the germ cells or gametes produced by cross-bred 
organisms may in respect of given characters be of the pure parental 
types and consequently incapable of transmitting the opposite char- 
acter.” (The italics are in the original.) This notion has also 
been expressed by others, or may be implied from their conclusions. 
Assuming such to be the case, how may we account morpholog- 
ically for the purity of the sex cells? 
Do the sex cells, which are thus shown by experiment to be 
‘ pure, arise by normal maturation mitoses, such as take place in pure 
taces, or are the divisions irregular, abnormal, and peculiar to each 
hybrid organism? It has, I think, generally been felt by botan- 
ists that the variations in the hybrids were, in some manner, con- 
; nected with that of the formation of the sex cells from which they 
arose, and this has apparently received cytological support. For 
_ instance, both Guyer, from his morphological studies of hybrid 
