iQigl MacDOUGAL, RICHARDS, 6= SPOEHR— SUCCULENCE 407 



based upon researches carried out with the fleshy plants.^ The 

 amount of detailed and systematic information concerning these 

 plants as a t>pe is probably greater than that of any other ecological 

 group, and it is evident that their metabolism presents some 

 definite characteristic aspects. It is upon the basis of such knowl- 

 edge that it becomes possible to formulate the generalizations set 

 forth in this paper. 



The only comparisons between succulents and non-succulents 

 that have been possible have lacked directness because the reactions 

 of different species could not be rated against each other with 

 accuracy. The final and necessary conditions for a critical dis- 

 cussion of the matter, that of succulent and non-succulent individ- 

 uals of the same species, finally came to the attention of the authors 

 in the case of Castilleja lalijolia at Carmel, California, in the summer 

 of 19 1 8. One form of this plant which grows on the edge of the 

 bluff overlooking the beach, or within 25 ft. of if, has succulent 

 leaves of considerable thickness which are usually pale green. The 

 other, which grows farther back on the foreshore, has a thinner, 

 mesophytic type of leaf which is darker green and more hirsute than 

 the succulent type. This is probably the t>'pical form of the 

 manuals and is similar to the one which grows farther back in the 

 pine woods. A notable exception as to the relative region of growth 

 of these 2 forms was found in a luxuriant growth of the thin-leaved 

 type at the base of the beach bluff on the edge of the sand. Exami- 

 nation showed that this was unquestionably due simply to the 

 ample water supply from the seepage at the base of the cHff. It 

 becomes evident, therefore, that the difference in the succulent and 

 mesophytic habit is not a case of even partial halophytism, for if salt 

 were present anywhere it would be at the chft" base. The contrast- 

 ing habit is one rather of xerophytism versus a mesophytic growth. 

 The members of the genus are reported to be parasitic, and 

 individuals with thin and others with succulent leaves were found 



^ Spoehr, H. a., Photochemische Vorgange bei der Diurnalen Entsaurung der 

 Succulenten. Biochem. Zeitsch. 57:95-111. 1913. 



Richards, H. M., Acidity and gas interchange in cacti. Publ. no. 209. Carnegie 

 Inst. Wash. 1915. 



Hempel, Jexxy, Buffer process in the metabolism of succulent plants. Compt. 

 Rend. Carlsberg. 13: no. i. 191 7. 



