ALISMACE^ 397 



Sagittarta 



Monoecious pollen flowers without nectar. 



S. sagittifolia (Arrowhead). — There are tViree kinds 

 of leaves. Those which are submerged are ribbon- 

 shaped ; the swimming ones, heart-shaped ; those which 

 rise into the air, arrow-shaped. The submerged leaves 

 are very thin, and, as Frank has shown,^ the chlorophyll 

 grains arrange themselves in the cell according to the 

 light, almost as in Lemna (see ante, p. 393). Moreover, 

 they are somewhat flat, and with the same object alter 

 their angle according to circumstances. The seeds are 

 shining, and are not wetted by water ; the result is 

 that they float on the surface and are dispersed by 

 currents. 



Alisma 



White or reddish flowers with half-concealed nectar, 

 secreted by a ring at the base of the stamens. There 

 are three British species. A. Plantago has numerous 

 flowers in a loose panicle. The other two have few 

 flowers. A. ranunculoides is an erect or creeping plant ; 

 A. natans floats. 



A. Plantago. — The flowers are homogamous ; the 

 anthers open outwards. They are principally visited 

 by flies. 



A. ranunculoides. — The secretion of nectar is less 

 abundant. 



A. natans. — A delicate floating plant very rare in 

 Britain. Owing to its difi"erence in habit it has been 

 regarded by some botanists as a distinct genus, Elisma. 



Damasonium 



D. stellatum (Star-fruit). — So called from the spread- 

 ing fruits. It is a Western Mediterranean plant, which 

 is sometimes found in gravelly ditches and pools in the 

 South of England. 



^ Prinssheim's Jahrhucher, 1872. 



