HERBERT JONES 189 



H 



2 3 4 5 12 



A B 



C D 



Fig. 1. Leaves of four species of Callitriche. 

 A. C. intermedia. 1 and 2 represent extremes of leaf form, 1 from a floating crown in still water and 2 from 

 a submerged crown in running water. 3, 4 and 5 are leaves from the same shoot, there being three nodes 

 between each leaf. Leaf 3 formed in a floating crown. The crown was then submerged and leaf 4 is the 

 result of early development under floating conditions and later development under submerged conditions. 

 The crown later arrived at the surface again and leaf 5 shows the influence of early development under sub- 

 merged conditions and later development under floating conditions. B. C. obtusangula. 1. Leaf from 

 floating crown. 2. Leaf from submerged axillary shoot. C. C. stagnalis. Leaf from floating crown. 

 D. C. hermaphroditica. Leaf from submerged crown. 



possible to have a leaf which is Unear in outline with 3 veins. The converse is not true, 

 however. As soon as an obovate leaf becomes discernible, the 3-veined condition occurs. 



Fruit form and styles (Fig. 2 A 1-4) 



Fruits 1-3 mm. long by 1-4 mm. broad. In face view the fruits are not narrowed 

 towards the base. Grooves and keels of medium development, the keels being parallel. 

 Styles are lateral, between 1 and 2 mm. long and fall early. All fruits which have been 

 observed in the Aberystwyth district over a period of some 9 years have been sessile. On 



