216 VEGETATIVE REPRODUCTION [CH. 



the water forms are perennial. In the aquatic Callitriches, 

 rooted internodes bearing lateral buds may remain in the mud 

 and tide over the winter 1 . Montia fontana^ also, is biennial in 

 places where the water is liable to dry up, but, in springs and 

 permanent streams, it grows strongly and becomes perennial 2 . 

 Those water plants which have not adopted special methods 

 of perenniation, generally retain their leaves through the winter, 

 e.g. Peplis Portula^ Ceratophyllum, Hottonia^ and the submerged 

 species of Callitriche. In the case of such plants, any detached 

 shoot will generally grow into a new individual with extreme 

 readiness. In Hottonia the branches forming a whorl below the 

 inflorescence become separated from the axis and give rise to 

 new plants in the spring 3 . The present writer has noticed that, 

 in the case of Peplis Portula and Ceratophyllum, the submerged 

 stems are very brittle, and, in the early autumn, quantities of 

 detached floating shoots may be observed. The behaviour of 

 Callitriche* is particularly striking, for in this case new plants 

 can be formed from a node with only a very small piece of inter- 

 node attached. Lawia xeylanica^ Tul. 5 , one of the Podostema- 

 ceae of Ceylon, can recommence its growth from any portion 

 of the thallus, however small, if it be submerged under favour- 

 able conditions, and other members of the family have a similar 

 power. A very notable capacity for vegetative multiplication 

 is exhibited by some Cruciferae. In the case of the North 

 American Nasturtium lacustre^^ the pinnately dissected, sub- 

 merged leaves become detached about the middle of August 

 and float at the surface of the water ; an adventitious bud arises 

 at the base of each leaf and develops into a new plant. The same 

 production of buds from foliar tissue has long been known in 

 Cardamine pratensis^ the Lady's Smock, where it can easily be 

 observed at various times of year (Fig. 141). On May 21, 

 1919, the present writer saw countless plantlets growing from 

 detached leaflets in a dyke in the fens near Lakenheath Lode. 



1 VaucherJ.P.(i84i)andLebel,E.(i863). 2 Royer,C. (1881-1883). 

 3 Prankerd, T. L. (1911). 4 Hegelmaier, F. (1864). 



5 Willis, J. C. (1902). 6 Foerste, A. F. (1889). 



