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 1 . This 

 confirms an earlier suggestion, made by an Italian writer 2 , 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 3 , who estimated that 

 a well-developed floating leaf of Nymphaea lutea was about eleven 

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

 Another Dicotyledon, Proserpinaca pa/ustris, which was in- 



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



3 Brand, F. (1894). 



