LECT. X.] ANATOMY OP LEAVES. 585 



pulp and the cuticle, which we described in the 

 Aloe (page 564) ; and in the leaf of the Mesem- 

 bryanthemum, under examination, we perceive 

 these tubes commencing immediately under the 

 cutis, and terminating generally in the cells of 

 the central pulp ; but sometimes in follicles, which 

 are both very irregular in form, and of very dif- 

 ferent dimensions. It is probable that part of the 

 fluid taken up from the atmosphere passes at once 

 into the central cells, the contents of which are 

 colourless, while another part remains in the tu- 

 bular cells, and undergoes that change, which is 

 the usual result of the agency of light on the 

 juices of all leaves exposed to its influence. The 

 green colour of the fluids contained in these cells, 

 marks out their limits, in a transverse section of 

 the leaf, even to the naked eye. 



The structure of the vessels in succulent dico- 

 tyledonous leaves is the same as in all other leaves. 

 The conducting vessels are spiral tubes, of the 

 same diameter at the apex as at the base of the 

 leaf; and the proper or returning vessels are mem- 

 branous, and apparently perforated, although their 

 transparency renders it difficult to determine their 

 real character. The ramifications are all given off 

 at acute angles ; and appear to be merely separa- 

 tions from the caulinar or petiolar cluster, as Dr. 

 Grew supposed was the case in all leaves ; at least 



