WHITE— STUDIES OF INHERITANCE IN PISUM. 543 



diseased cotyledons, partially successful attacks of strangling fungi, 

 temperature and humidity variation, lack of sunlight, variation in 

 soil richness, etc. Dwarfing of tall varieties may be brought about 

 and the flowering period delayed as much as three weeks (26) by 

 cutting ofif part of the cotyledon in germinating peas. Lock (54) 

 found the climate of Perideniya directly modified the height and 

 growth habit of various varieties of English peas with which he 

 experimented. Further the difference between the height charac- 

 ters of the Ceylon-grown English peas and the same varieties grown 

 in England remained constant through five generations. At the 

 Brooklyn Botanic Garden, Black Abyssinian peas when grown in 

 the field plots bloom early and reach a height of never more than 

 60 cm. while under greenhouse conditions in the winter time under a 

 temperature of 48° F.-55° F. and growing two plants per 10 cm. 

 pot, they reach a height of over 120 cm. 



Height is best described in terms of internode length and num- 

 ber, and stem diameter, as in reality the length of a plant stem is 

 due to various combinations of these three elements. Described by 

 this method, and only taking into consideration height in peas under 

 the general climatic and soil conditions of Long Island, it appears 

 best to modify the height ranges assigned to tails, half dwarfs and 

 dwarfs as given by Bateson (i) and Keeble (49). 



Tall peas (150-360 cm.) have robust stems made up of a large 

 number (40-60) of short internodes or a much lesser number (20- 

 47) of long internodes. This class also has very long roots (i). 



Half-dzvarfs (60-150 cm.) have either robust or delicate stems 

 made up of a small number (10-24) of long internodes or a larger 

 number (20-40) of short internodes. This class is very unsatisfac- 

 tory, as it represents a very large number of diverse intermediate 

 types. 



Dzmrfs (23-60 cm.) have either robust or delicate stems made 

 up of a comparatively small number (8-18) of short internodes. 

 This group is easily and accurately distinguished from either of 

 the above, even in young stages 3 weeks or so old. 



