[ 9 ] 



CHAPTER II 



THE LIFE-HISTORY OF THE 

 ALISMACEAE 



THE Alismaceae^ are perhaps the most typically amphi- 

 bious of all water plants and they vary in appearance 

 according to their environment in a thoroughly protean fashion. 

 The Arrowhead, Sagittaria sagittifolia, L., may be chosen for 

 description as a characteristic member of the family. Seen in 

 ditches and backwaters in the late summer, its fine sagittate 

 leaves and bold inflorescences^ (Fig. i, p. lo) make it one of the 

 most striking of our water plants. It is apparently insect polli- 

 nated, but the records on the subject seem to be confined to the 

 statement that, in the Low Countries, certain species of Fly have 

 been observed to visit the flowers^. The present writer has once 

 noticed a Water-snail crawling over a female flower and engaged 

 in eating the perianth; it is conceivable that these animals may 

 play an occasional part in pollination. The large fruits, whose 

 hassock-shaped receptacles are completely clothed with com- 

 pressed, winged achenes, give the plant a highly individual 

 character (Fig. 2, p. lo). 



In complete contrast to the flowering form, is the guise 

 which the Arrowhead assumes in deep and rapidly-flowing 

 water. As long ago as 1596^ a tuber, bearing strap-shaped 

 leaves, was described by Gaspard Bauhin under the name of 

 "Gramen bulbosum," while in 1 620^ he published a figure of it, 



1 For a systematic review of the Alismaceae see Buchenau, F. (1903^), 

 and, for a general study of their life-history, Gluck, H. (1905); Gluck's 

 work has been largely drawn upon in the present chapter. 



2 On the detailed structure of the reproductive organs see Schaffner, 

 J. H. (1897). 3 MacLeod, J. (1893). 



4 Bauhin, G. ( 1 596). ^ Ibid. ( 1 620). 



