Caroline Pellew and Eva Richardson Sansomb 21 



foKage is broad and flat, the leaves trimcated at the tips but in the later 

 stages of growth more pointed, the stipules flat and rounded at the tips. 

 Both leaves and stipules are slightly marbled, the pale areas being 

 caused by air spaces below the epidermis (Fig. 1). The variety possesses 

 the following MendeUan factors, already studied by geneticists : round, 

 yellow cotyledons, black hilum, light axil, stumpy pod, brown-marbled 

 testa (known as "maple" pattern), and, in Th. 7, the factor for self- 

 coloured testa. In addition to the above there are certainly a number 

 of less well-known factors which, by crossing with the appropriate 

 varieties, could be identified and analysed. 



It is probable that the most significant difierence between the Thibet 

 pea and our own varieties is the small size of the whole plant. From the 

 observations of Vavilov (1926) it appears that all Asiatic peas are small 

 compared to European varieties. Among our own varieties we find great 

 differences in size, but we have scarcely any information on the genetical 

 factors involved in these differences. Mendel's factors for "tallness" and 

 "dwarfness" influence the length of the internodes, but there appear to 

 be corresponding varieties of different "size" among the tails and the 

 dwarfs, and we do not know of any correlated effect produced by these 

 factors. My own observations point to there being many factors having 

 an influence on the size of different parts of the plant, but their effects 

 are probably controlled by certain developmental factors, for instance 

 time of flowering and length of growing period. Hence actual measure- 

 ments of any particular organ appear to be of little value until the 

 correlated effects of such developmental factors are better understood. 



The foliage of the Thibet pea is especially interesting, being inter- 

 mediate between the broad, truncate fohage of the "type" form of our 

 most widely cultivated varieties, and the narrow pointed fohage of the 

 "rabbit-ear rogues" occasionally thrown by such types (Bateson and 

 Pellew, 1915, 1920). It corresponds on a small scale to that of the 

 Mummy pea, a kind of foliage which has been shown to have approxi- 

 mately normal relations to that of both types and rogues (Brotherton, 

 1923). For this reason it was decided to cross the Thibetan pea with the 

 type and also with the rogue of one of our most widely cultivated 

 varieties, Duke of Albany, and to study the various factors introduced 

 by the Thibetan pea in relation to the different kinds of foliage. The 

 observations bearing on this part of the experiment are not complete, 

 but it may be stated that there is a possibility of a relation, the nature 

 of which is still obscure, between the different kinds of foliage and the 

 factors associated with the chromosome ring. 



