ii] THE WATER PLANTAIN 19 



be attached to this observation, which, as its author points out, 

 suggests a case of auto-parasitism. 



After the Arrowhead, probably the best known British 

 member of the Alismaceae 

 is the Water Plantain, 

 Alisma Plantago^ L. 1 Ac- 

 cording to modern views 2 , 

 this Linnean species in- 

 cludes two plants which 

 are each worthy of spe- 

 cific rank Alisma Plan- 

 tago^ (L.) Michalet, and 

 A. graminifolium, Ehrh. 

 The former is more suited 

 to land life, while the 

 latter is typically a water 

 plant. A. PlantagO) (L.) 



Mich, generally lives in FIG. 8. Sagittaria sagUtifolia, L. Diaphragm (D) 

 , n 1 of petiole in transverse section. T = wall of 



shallow water, where air la ^ una . L = lacuna [BlanCj M le (igi2) ^ 

 leaves form the chief as- 



similatory organs. These are preceded, however, by band-shaped 

 primary leaves (Fig. 101 #, p. 153) and then generally some 

 swimming leaves (Fig. 102, p. 1 53), so that the Water Plantain, 

 like the Arrowhead, produces three distinct types of leaf. In 

 dark situations the swimming leaves may be replaced by sub- 

 merged leaves differing from the ordinary submerged band-leaves 

 in possessing a distinct lamina. This species only flowers suc- 

 cessfully in relatively shallow water in which air leaves can be 

 produced; in moderately deep water, in which submerged and 

 swimming leaves occur, a reduced inflorescence is occasionally 

 formed, but, in very deep water, where all the leaves are band- 

 shaped and submerged, flowers are always absent. Alisma 

 graminifolium^ on the other hand, has its optimum growth in 



1 On the details of fertilisation, etc., in this species see Schaffner, J. H. 

 (1896). 



2 Gluck, H. (1905). 



2 2 



