On Mendel's Laws . 
223 
whole period of the experiments. They remained constant without 
any exception. ” The races for crossing were thus chosen with the 
greatest care and patience so as to be absolutely distinct; an A 
individual mated with an A never producing as, nor vice-versa, for, 
as I understand, the whole period of ten years (two years of 
preliminary trials and eight years of experiment.) 
Mendel’s observations, as most of the readers of these articles 
will be aware, revealed several distinct uniformities, the verbal 
description of any one of which might be legitimately entitled a 
“ Mendel’s Law.” When the two parent races A and a were 
crossed, their mongrel or hybrid offspring resembled uniformly 
either the A’s or the as —say the former, in which case A was 
termed the dominant character, a the recessive. When these first 
uniform hybrids were crossed inter se, the resulting offspring were 
no longer uniform but broke up again into two classes resembling 
the parent races—approximately three-fourths exhibiting the domi¬ 
nant character and one-fourth the recessive. The whole of these 
“ extracted ” recessives—to use Mr. Bateson’s convenient term¬ 
inology—breed pure, i.e. never give rise again to the dominant 
form. Of the dominants, however, only one-third breed pure, 
the remainder giving rise again to dominants and recessives in 
the proportion of three to one. These remarkable results 
Mendel explained by a hypothesis which certainly appears, for 
the case of a single character, of most attractive simplicity. He 
supposed that a sorting process takes place during the formation 
of the germ cells of the A a hybrids, of such a nature that each 
finally formed gamete, without exception, only contains the germinal 
representative of either the A -character or the ^-character, and 
that conjugation between A -gametes and rt-gametes takes place at 
random. The result is that the zygotes A A, A a, a A , andaa are all formed 
with equal frequency. But the heterozygotes (to use Mr. Bateson’s 
terminology again) both give rise to individuals resembling the 
pure dominant form. The offspring therefore exhibit three 
dominant forms (one pure and two hybrids) to one recessive 
(necessarily pure). 
This law of disjunction, or “segregation,” Mendel tested 
also for pairs and triplets of characters. The results obtained 
for one character alone leave it open to question whether the 
group of characters (represented by the germ-plasm, chromatin 
or whatever it may be) derived from the one parent, has separated 
bodily from that derived from the other, or whether any more 
