40 



THE VEGETABLE CELL IN GENERAL. 



appear to be much like the sphere-crystals described in 186. But 

 if they are carefully treated with dilute hydrochloric acid, the 

 chief part of the concretion disappears, leaving behind a delicate 

 trace of cellulose which was intermingled 

 with it. That this cellulose was an in- 

 trusive growth into the cell from the 

 wall, is shown by a study of its develop- 

 ment. In most cases such concretions 

 (Cystoliths) are plainly stalked, but in 

 some instances they are only obscurely 

 stalked, and are with difficulty distin- 

 guished from the ordinary cell concre- 

 tions. In the leaf of Ficus elastica (sec 

 Fig. 6) they are more completely devel- 

 oped than in any other common plant. 



165. Other changes, chiefly those of 

 degradation, may take place in the cell- 

 wall, giving rise to products variously 



known as gums, resins, &c. ; but in all these cases there is such 

 a commingling of the cellulose derivatives with those formed 

 from the contents of the cell, that they cannot be readily dis- 

 tinguished. 



166. Protoplasm, as was shown in the previous sections, gives 

 rise upon its exterior to the cell-wall. Inside the cell, likewise, 

 it produces, either directly or indirectly, various substances. In 

 the present chapter these substances are to be considered only so 

 far as relates to their detection and identification. Most of them 

 are to be examined later, with reference to their office in the life 

 of plants. 



167. Plastids. In the protoplasm of active cells certain gran- 

 ules having substantially the same chemical and, with the excep- 

 tion of their color, the same physical properties as protoplasm, 

 are clearly differentiated. They are imbedded in the general 

 protoplasmic mass, and are not separable from it by mechanical 

 means. 



168. Such granules may be conveniently referred to three 

 types, 1 depending upon the color : (1) those which are green, 



1 Recent investigations render it probable that these three kinds of granules 

 are derived from a common source, and although hardly distinguishable from 

 Fio. 6. CystoHth from the upper part of a leaf of Ficn* olantlca e, epidermis; 

 y CC> <7St0mi1 ; Ch ' rh - Cells *nn* elilorophvll. It will he observed 



the cy ' tolitl1 ""P""" to * tt * "> * '" * of the upper 



