108 LOCK : PRESENT STATE OF 



The behaviour of the colour characters of the testa ajicl 

 corolla have now been worked out completely, and described 

 in terms of Mendelian segregation witlx the help of the idea of 

 the masking of certain characters when certain other charac- 

 ters are absent. 



The principal gaps now remaining in our knowledge relate 

 to the heredity of the purple pod and of the allelomorphs 

 concerned in determining the number and length of internodes. 



From De Candolle's remarks in his Origin of Cultivated 

 Plants he does not seem to bo aware of the maple type of pea 

 with smooth seeds, and he follows the long established error 

 of distinguishing Pisum arvense and P. sativum as separate 

 species. Darwin states that an extinct variety of pea with 

 very small round seeds allied to the field pea is recorded from 

 the lake dwellings of Switzerland. 



After examining the wild pea, seeds of which were brought 

 from Palestine by a member of the firm of Sutton & Sons, 

 and comparing it with a closely similar plant growing in India 

 and Ceylon, the behaviour of which on crossing has been 

 studied in some detail, a near idea of the appearance of the 

 original wild type of the cultivated species of Pisum has, it is 

 thought, been obtained. It is of interest that the dominant 

 member of the pair represents the primitive character in at 

 least 12 out of the 13 cases of allelomorphic pairs which can 

 confidently be claimed as such. The doubtful case is that of 

 the dimpled character, as there is some uncertainty as to 

 whether the primitive type was dimpled or smooth. All the 

 most primitive types of peas known have smooth seeds, and 

 the uncertainty chiefly arises from the fact that all the other 

 primitive characters are dominant. 



Xenia. — Bateson records good instances of this phenomenon 

 when green peas with greenish skins are crossed with yellows 

 — yellow cotyledons and yellowish skins. The testas of the 

 resulting seeds turn yellow like the cotyledons. The white 

 peas which I have examined have mostly had nearly coloui'less 

 testas, and the phenomenon of xenia was not observed. 



In this connection reference may be made to a phenomenon 

 which it seems fair to describe as practically the reverse of 

 xenia. That is to say, the-direct effect of the maternal charao- 



