2i6 VEGETATIVE REPRODUCTION [ch. 



the water forms are perennial. In the aquatic CalHtriches, 

 rooted internodes bearing lateral buds may remain in the mud 

 and tide over the winter^. Montia jontana^ 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^. 

 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^. 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 zeylanica^ Tul.^, 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, 

 1 91 9, 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). ^ Royer, 0.(1881-1883). 

 3 Prankerd, T. L. (191 1). ^ Hegelmaier, F. (1864). 



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



