MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 299 



was maintained for a time after being exposed to light, but eventually 

 the plants which had been normally illuminated reached the greatest 

 length of stem. The internodes which developed on etiolated stems 

 immediately after exposure to light were something shorter than 

 homologous members of normall}' illuminated shoots. During the 

 process of transferring etiolated plants from darkness to light many 

 leaves and often portions of the shoot were killed by reason of the 



Fig. 176. Hicimts communis. A^ normal epidermis from ventral (upper) sur- 

 face of leaf; B, epidermis from ventral surface of etiolated leaf. After Ricome. 



desiccation consequent upon the accelerated transpiration. The re- 

 tarded growth of the younger portions upon illumination was ascribed 

 to this exaggerated loss of water. Upon the illumination of etiolated 

 seedlings the new processes including differentiation of the tissues 

 and of a generative layer set up such tensions in the cortex and epi- 

 dermis that these tissues were not able to keep pace with the exten- 

 sions and were ruptured and crushed. Ricome did not regard 

 etiolated organs as pathological, because of the fact that after illumi- 

 nation they were capable of carrying out a development fairly ap- 

 proximate to that of the normal if a proper supply of constructive 

 material were provided. Thus, in the case oiRicinus, leaves formed 

 under etiolative conditions were seen to attain a size in excess of the 

 normal in some instances when illuminated. In no instance does 

 this author find any warrant for an assumption that the action of light 

 retards growth, although the length attained by internodes and organs 

 might be less by reason of the actual desiccation consequent upon 

 increased transpiration caused by light. 



