CUTICLE. 33 



oped vcfictables. If wc take a tree for instance, we find it com- 

 |)osod of various well defined parts ; and to dcscril)C a tree, 

 takinn- it part by j)art, wc sliall describe all tlic compound 

 organs wliicli go to form tbc wbole vegetable kingdom. We 

 find it in tbc first place, covered in its earliest stage at least, 

 by a thin membrane extending over tbc wbole surface from 

 the deej)est root to the iiigbest leaf, called the cuticle. Within 

 this covering we find another distinct zone, called the hark ; 

 within the bark we find the main axis of the plant called the 

 ircxW, which is composed of two portions, one ascending, and 

 called the stcm^ the other descending, and termed tbc root. 

 Within the stem we tind a sol't spongy substance, denomi- 

 nated the pith. To the root and stem are attached branches, 

 and to those of the stem are attached leaves, flowers and 

 fruit. 



We shall describe the above organs in the order laid down. 



Section 1. — Cuticle. 



37. The cuticle is composed of flattened cells,[adlicring tO 

 each other by their edges, and forming a continuous covering 

 over the whole plant, except the stigmatic surface, spongioles 

 and parts growing under water, and is generally composed of 

 a single layer of cells, but sometimes in succulent plants of 

 two or more layers. The cuticle of the Oleander is composed 

 of three or four layers of thick sided cells. The joining lines of 

 the cells may be seen on the leaves of plants by the microscope, 

 presenting, generally, hexagonal figures more or less regular. 

 Sometimes, however, the lines produce irregular figures, assign, 

 able to no geometrical form. The cuticle may be easily sep- 

 arated iVom the subjacent layer of the leaves of the iris or 

 lily, by means of a sharp knife, and examined in water by 

 the microscope. If the microscope be good, the cellular ca- 

 vities will be easily seen, otlierwise the tlattened surface only 

 can be distinguished. It seems to be pretty well established 

 at the present time, that over the cuticle there is a covering 

 of organic mucus, extending over not only the cuticle proper, 

 but over its most minute appendages, the finest hairs. It has 

 Ijeen demonstrated in many instances, and no doubt is an uni- 

 versal fact. 



38. On the lines which separate the cells that compose the 

 cuticle, small oval spaces are observed, which are called sto- 

 mates, in allusion to the function they are supposed to perform, 

 that of mouths through which the plant respires. These stoma- 

 tes are curiously constructed, generally consisting of two 



