186 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 



