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CHAPTER IV 



THE LIFE-HISTORY OF HTDROCHJRIS, 

 STRATI OTES, AND OTHER FRESH-WATER 

 HYDROCHARITACEAE 



A BIOLOGICAL classification of water plants, such as 

 that outlined in Chapter i, has little in common with 

 any phyletic scheme. The incompatibility between biological 

 and phylogenetic systems is particularly well illustrated in the 

 Hydrocharitaceae, which include besides some marine ge- 

 nera both marsh or shallow-water plants with air leaves, sub- 

 merged plants and floating plants. As an example of the latter 

 we may choose the Frogbit, Hydrocharis Morsus-ranae^ the only 

 British plant with typical floating leaves which swims freely in the 

 water. Other members of the genus however, e.g., H. asiatica}- 

 and H.parnassifolia'^^ have air leaves. In the case of H. Morsus- 

 ranae it is possible to produce a land form artificially^, and this 

 form has also been recorded on one occasion in nature'*. 



In places where the Frogbit flourishes, the surfaces of the 

 ditches and dykes which it inhabits are often completely covered 

 by its leaves, which resemble a miniature edition of those of the 

 White Waterlily. These leaves are produced in rosettes from a 

 tiny, abbreviated stem, which gives rise during the summer to 

 numerous lateral stolons, each ending in a rosette similar to the 

 parent, and repeating the production of stolons da capo. At the 

 base of each rosette, a number of roots of a greenish colour are 

 produced. They hang down into the water, but do not enter 

 the substratum except occasionally in the shallows^. These 

 roots bear, along the greater part of their length, a very large 

 number of unusually long root-hairs, which are well known as 



1 Solereder, H. (1913). 2 Solereder, H. (1914). ^ Mer, t. (1882I). 

 ^ Gluck, H. (1906). 5 Goebel, K. (i 891-1893). 



