W. Neilson Jones and M. Chevelv Rayner 215 



C. Anatomy of Shoot. 



In transverse sections of the aerial shoots of B. dioicu the vascular 

 biuulles — which vary eonsiderably in size in difierent regions of the 

 stem — are arranged in two rings. 



This arrangement is a general one in the Natural Order Cucurbi- 

 taceae and the anatomical details have been described for various 

 genera including Bryonia (8, 9). 



The total number of bundles is recorded as 10 for various 

 genera, but deviations from the 5 + arrangement are noted, and 

 de Bary (10) mentions seven as the characteristic number in the outer 

 ring of bundles in B. dioica. 



The stems are ridged externally to correspond with the number of 

 bundles in the outer ring, and the number of bundles in cross section 

 can be readily determined by examination with a pocket lens. 



We have found a constant and distinctive difference with regard to 

 the number of stem bundles in our varieties, and have recorded their 

 genetical behaviour when bred together. 



At the base of the shoot close to the tuber, the total number 

 of bundles is small — often eight or fewer. 



As the distance from the tuber becomes greater, the number of 

 bundles present in transverse section increases gradually to a maximum, 

 the arrangement in two rings being maintained. 



These maxima differ in the two varieties under consideration, this 

 statement being based on a large number of observations on many 

 different plants. 



In variet}' G the number of bundles gradually increases up to ten, 

 arranged in two rings of five each. However long or vigorous the shoot, 

 this number is not exceeded in any part of the successive intemodes. 

 Fig. 5 (c). 



In variety B, on the other hand, the number of bundles increases to 

 14 an-anged in two rings of seven each. Fig. 5 («, b). 



Correlated with this difference in number, the external ridges on 

 the stem are respectively five and seven for the two varieties. 



The possession of a shoot or some part of a shoot having fewer than 

 14 bundles does not preclude a plant from belonging to variety B in 

 this respect. Fig. 5 (6). 



The difference between the two varieties lies in the capacity of 

 variety B to increase the number of bundles beyond ten as seen in 

 transverse section. Although every shoot on the plant may not show 



