MENDELIAN CHARACTERS IN PLANTS AND ANIMALS, il 
characters may well be: (1) presence (R) and absence (r) of rose; (2) 
presence (LL) and absence (1) of leaf; presence being dominant to absence 
in both cases, single (S) being common to both. In that case the gametic 
formula fears comb may be regeried as (R+1+S8), and that of leaf comb 
as (L+r+5). 
These results confirm the similar experiments and conclusions of 
Messrs. Bateson and Punnett with rose and pea combs. 
Tt seems clear, therefore, that the pure-breeding rose comb of the 
‘Black Hamburgh’ fowl is a compound character represented in the 
gametes by at least two distinct factors. 
THe NATURE OF MENDELIAN CHARACTERS. 
The foregoing illustrations show some of the difficulties encountered 
by the experimenter in the determination of Mendelian characters in 
plants and animals. It is evident that the precise determination of unit- 
characters can only be secured by means of careful and exhaustive experi- 
ments. 
‘When we find such apparently simple zygotic characters as those 
noted above giving a simple Mendelian result in certain crosses and yet 
in others proving to be gametically compound, the question naturally 
arises whether many other of the apparently simple Mendelian characters 
are not also compound in their gametic constitution. 
Is it not possible, for instance, that some of the original Mendelian 
characters in peas may be due to more than one gametic factor ? 
For example, in cotyledon colours in peas, might not the character 
pairs be really presence and absence of yellow on a basis of green, rather 
than the contrasting yellow and green? Is it not possible that many of 
the so-called contrasting pairs of Mendelian characters are really com- 
pound, and that the true unit-characters are simply presence and absence ? 
REVIEW OF EXPERIMENTS. 
In view of the possible reduction of Mendelian characters in plants 
and animals to the simple presence and absence of unit-characters, it may 
be useful to review briefly the Mendelian characters found in my own 
experiments. 
PEAS. 
In my experiments with peas, the Mendelian characters met with are 
the same as those discovered by Mendel, viz. yellow and green cotyledons, 
round and wrinkled seeds, tall and dwarf stems—the first-named of the 
pair being dominant over the other, which is recessive. As suggested 
above, the Mendelian contrasting pair, yellow and green, might be 
_ regarded as presence and absence of yellow on a basis of green. On 
_ this view, the characters yellow and green would belong to two distinct 
pairs, instead of one as Mendel supposed, and these would be presence 
_ (Y) and absence (y) of yellow, and presence (G) and absence (g) of green, 
presence being dominant oyer absence. The gametic formula of the 
E pure-breeding yellow pea based on green would, on this view be (Y+G), 
and the zygote yellow owing to dominance. 
