OSMOTIC GROWTH 



143 



The foliaceous expansions, or osmotic leaves, also present 

 great varieties both of appearance and of structure. The 

 veins may be longitudinal, fan-shaped, or pcnniform. We 

 have occasionally met with leaves having a lined or ruled 

 surface, giving most beautiful diffraction colours. The usual 

 structure, however, is vesicular or cellular, as in Fig. 58. In 



Fig. 57. — Photograph of an osmotic lea! 

 showing the veins. 



photographs we often get the appearance of lacunas, but all 

 these lacuna? are closed cavities, the appearance being due to 

 the transparency of the cell walls. 



In conclusion we may say that osmotic growths are formed 

 of an ensemble of closed cavities of various forms, containing 

 liquids and separated by osmotic membranes, constituting 

 veritable tissues. This structure offers the closest resem- 



