198 LAND AND WATER FORMS [CH. 



the plant reaches its optimum development as an aquatic, 

 and flowers freely in water. As a land plant it rarely blossoms 

 and, indeed, under xerophilous conditions, flowering seems to 

 be entirely inhibited 1 . 



In the case of amphibious plants, which can produce land 

 or water forms according to circumstances, the difference in 

 external appearance is often very 

 marked. Limosella aquatica, for 

 instance, produces a land form 

 with leaf-stalks half-an-inch to 

 one inch long, while the water 

 form may have petioles six inches 

 long, terminating in tender trans- 

 lucent blades 2 . Littorella lacustris 

 is another striking example. The 

 shallow water form, deep water 

 form, and land form are shown 

 in Fig. 128 A, B and C. 



Various land plants can grow 

 and flower freely with their roots 

 and the lower parts of their stems 

 actually under water; Solanum 

 Dulcamara (Bittersweet) is a 

 species to which these condi- 

 tions seem especially favourable. 

 Such plants form a transition to 

 those which frequent the margins 

 of fresh waters, and are capable of responding to changes in the 

 water level by producing, at need, actual aquatic forms. Gliick 3 , 

 who has given great attention to this subject, has shown that, in 

 nature, submerged forms, often with reduced vegetative organs, 

 are produced not only by plants which normally inhabit damp or 

 marshy situations, such as Ranunculus Flammula (Figs. 1 34 and 

 1 35> P' 2O 3)> Ca/thapa/ustris(Fig. 129), Cnicuspratensis* (Fig. 1 30 



FIG. 128. Littorella lacustris, L. (=L. 

 juncea, Berg.). A and B, water 

 forms; C, land form. A is from water 

 30 to 40 cms. deep ; B is from water 

 100 cms. deep; C shows three male 

 flowers one of which has lost its 

 stamens. (Reduced.) [After Gliick, H. 

 (1911), Wasser- und Sumpfgewachse, 

 Bd. in, Fig. 34, p. 346.] 



1 Massart, J. (1910). 

 Clack, H. (191 1). 



2 Schenck, H. (1885). 

 4 Gliick uses the name Cirsium anglicum> D.C. 



