20 ALISMACEAE [CH. 



deeper water than A. Plantago and is capable of flowering at a 

 stage when it bears band-shaped leaves alone. It was figured in 

 this condition by Loeselius 1 , more than two hundred years ago, 

 under the name of "Plantago aquatica." It never, either in the 

 seedling or adult form, produces floating leaves. It grows and 

 flowers best in 50 to 70 cms. of water; at a greater depth 

 (2 to 4 metres) flowering is inhibited. In spite of the marked 

 tendency of this species towards a strictly aquatic life, a land 

 form can be obtained in cultivation ; this proves to be identical 

 with the plant, sometimes found wild, which has been called 

 Alisma arcuatum^ Mich. 



Another closely related genus is represented by the pretty 

 little Echinodorus ranunculoides, whose different forms can be 

 observed, among many other water plants, at Wicken Fen near 

 Cambridge an untouched fragment of fenland, which has re- 

 tained many of its primitive features. Fig. 9 C shows the young 

 aquatic form, with both narrow submerged leaves and leaves 

 with floating blades. An entirely submerged form has been 

 described, which may flower under water at a depth of three 

 feet 2 . Fig. 9 B shows the luxuriance which the mature plant 

 may attain, when it grows in water, but raises its leaves and 

 flowers into the air, while Fig. 9 A indicates the general dwarf- 

 ing of the land form. Fig. 147, p. 224, shows the transitions 

 which sometimes occur in this species between inflorescences 

 and entirely vegetative rosettes. The related genus Elisma, 

 with its single species, E. natans^ (L.) Buchenau, is chiefly in- 

 teresting on account of a similar intimate relationship between 

 the inflorescence and the vegetative shoot. The bracts of the 

 inflorescence are in whorls of three ; flowers typically arise in 

 the axils of two of the bracts, while a leafy shoot is developed in 

 the axil of the third. The inflorescences are thus partly repro- 

 ductive and partly vegetative; there are also certain purely 

 vegetative off-shoots, which may be interpreted, in a morpho- 

 logical sense, as inflorescences which have become wholly 

 sterile. 



1 Loeselius, J. (1703). 2 West, G. (1910). 



