108 MENDELISM 
may take the case of the wrinkled sugary type of maize 
already contrasted with the smooth starchy variety. 
The essential difference between the two kinds depends 
upon the fact that in the former the reserve product 
laid down in the endosperm is different, being largely 
of a sugary nature instead of being starchy. With 
this circumstance is associated the presence of a larger 
proportion of water in the unripe grain. And the 
result of this is that, when the grain dries, its surface 
falls into folds. The sugary nature of the grains also 
causes them to take on a more hyaline or semi- 
transparent appearance than the grains of the starchy 
variety. All these characters, if they can be so called, 
behave on crossing as a single Mendelian allelomorph, 
and are doubtless represented in the germ cells by a 
single substantive representative. 
A simple example of what may probably be regarded 
as a real case of coupling is afforded by certain colour 
characters exhibited by pea-plants. In these plants 
coloured flowers, a red or purple colouration in the 
axils of the leaves, and a marked pigmentation of the 
testas, or seed-coats, are always associated together on 
the same plants ; so that, if we find a plant which has 
green leaf axils, we may be sure that its flowers will 
be white, and the testas of its seeds only slightly pig- 
mented. On crossing plants bearing coloured axils, 
coloured flowers, and pigmented testas, on the one 
hand, with plants bearing green axils, white flowers, 
and unpigmented seed-coats, on the other, the two sets 
of characters are found to behave as a simple pair of 
allelomorphs, and the simultaneous appearance of 
