[From JOURNAL OF GENETICS, Vol. xxv. No. 1, 

 pp. 25-54, NovBMEEE, 1931.] 

 • [All rights reserved} 



GENETICAL AND CYTOLOGICAL STUDIES 0*N THE 



RELATIONS BETWEEN ASIATIC AND EUROPEAN 



VARIETIES OF PI8UM SATIVUM. 



I. PAETIAL STERILITY IN HYBRIDS OF A THIBETAN AND 

 A EUROPEAN VARIETY. 



By CAROLINE PELLEW. 



II. CHROMOSOME ASSOCIATION EST PI8UM. 



By EVA RICHARDSON SANSOME. 

 (The John Innes Horticultural Institution, Merton.) 



(With Twelve Text-figures.) 



PAET I. 



Introduction. 



About the year 1922 a variety of Pisum sativum cultivated in Thibet was 

 introduced into this country, probably by members of the Mt Everest 

 Expedition. It differs in a very striking degree from our own cultivated 

 peas, possessing as it does some of the chief characters by which Asiatic 

 forms differ from those of Europe. Little is known of the genetical relations 

 between such forms, and these experiments were begun in the hope that 

 the Thibetan variety would prove to be favourable for a more extensive 

 investigation than had hitherto been attempted. The preliminary results 

 have been encouraging, for with one exception the fertility of the hybrids 

 is complete, or almost complete. The exceptional case arises when a par- 

 ticular "line" of the Thibetan pea is crossed with our own varieties; the 

 hybrids are then partially sterile. The partial (gametic) steriUty of these 

 hybrids has been found by Mrs Sansome to be associated with the formation 

 of a ring of four chromosomes in the reduction division (E. Richardson, 

 1929). In this paper certain genetical phenomena, connected with the 

 ring, wiU be described. Although the experiments as a whole are in- 

 complete, it seems desirable to pubUsh this preliminary account, in view 

 of the slight information we possess of the genetical effects of ring 

 formation in diploid plants. 



Our original stock of the Thibetan pea came from Prof. Engledow 

 who, in 1925, sent some packets of seed to Mr Bateson with the following 



