54 HYDROCHARITACEAE [CH. 



as so abundant as to be a troublesome weed, the plantlets sur- 

 viving the hardest winter 1 . 



In the great majority of localities the continued existence of 

 Stratiotes depends absolutely upon bud-formation, since the 

 plant is dioecious, and only in a small part of its range is it 

 found with both male and female flowers. In England only the 

 female plant is usually met with (Fig. 33). There are some 

 records of the occurrence of hermaphrodite flowers 2 , but ripe 



fa--' 



A B C 



FIG. 33. Stratiotes aloides, L. A, unopened female flower emerging from two 



bracts (6). B, female flower with bracts and perianth removed to show ovary (o), 



stigmas (st.) of which there are six, each bifurcated to base, and staminodes (sta.). 



C, unfertilised fruit (o) emerging obliquely from the bracts. [A. A.] 



seed does not seem to be formed in this country at the present 

 day, though fruits with seeds are known from Pliocene and 

 Pleistocene deposits 3 . The geographical distribution of the 

 sexes is rather curious. According to Nolte 4 , in the northerly 

 part of the range of the species only female plants occur, while 

 at the southern extremity the plants are either predominantly 

 or entirely male. In an intermediate area both sexes occur. 

 In addition to the Frogbit and the Water Soldier, Hydrilla 



1 Klinsmann,F.(i86o). 2 Geldart, A.M. (1906). 3 Reid, .(1893). 

 4 Nolte, E. F. (1825); see also Caspary, R. (1875). 



