xi] WATER LEAVES AND LOW VITALITY 159 



the same way as the Monocotyledons already mentioned. In the 

 case of two species of Castalia^ it has been found possible to 

 induce the mature plants to form submerged leaves, either by 

 removing the floating leaves or by cutting off the roots^. This 

 confirms an earlier suggestion, made by an Italian writer^, that 

 the development of the submerged leaves of Nymphaea lutea 



Fig. 105. Potamogeton natans, L. The uppermost internodes of a normal plant 



grown as a cutting. One floating leaf (s) survives, while the axillary shoots have 



produced leaves with thin narrow blades, representing a transition between the 



floating and submerged types. [Esenbeck, E. (1914).] 



was due to "un indebolimento o diminuzione di energia 

 vitale." This suggestion has received independent, experi- 

 mental confirmation from another worker^, who estimated that 

 a well-developed floating \e3.f of Nymphaea lutea was about eleven 

 times the dry weight of a submerged leaf of the same area. 

 Another Dicotyledon, Proserpinaca palustris^ which was in- 



1 Wachter, W. (18972). 2 Arcangeli, G. (1890). 



3 Brand, F. (1894). 



