MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



'37 



A notable feature of the behavior of succulents in darkness is 

 their great endurance to exclusion from illumination, and also their 

 capacity for the maintenance of chlorophyl for extended periods in 

 the organs constructed in light. The reactions offered by Gasteria, 

 of which the excessive lengthening of the stem is the most important 

 are also to be seen in the Crassulaceae as examined by Brenner'"* 

 and others. This author found that the growth of species of this 

 family in moist chambers produced an excessive elongation of the 

 stems, which continued only for a time, when the habit of developing 

 short internodes and consequent rosettes of leaves was again resumed. 



Fig. 167. Sempervivum assimile. A, normal; B, grown in a moist cliamber; C, 

 grown in a dark room. Redrawn, after Brenner. 



The effort in question may be fairly interpreted as a response to the 

 increased humidity, the increased surface offering additional facilities 

 for transpiration. 



The formation of slender cylindrical stems instead of the normal 

 flattened '* joints " seen in Opiintia O^untia, O. leucotrichia and some 

 other Cactaceae is not exhibited by all plants of this general char- 

 acter, however. Thus the leaf-like shoots of Phyllocaciiis latifrons 

 do not lose their bilateral form and organization, although reaching a 



''^ Brenner, W. Untersuchungen an einigen Fettpflanzen. Flora. 87: 387. 1900. 



