136 VEGETABLE LIFE AND GROWTH. [SECTION 16. 



§ 2. CELL-CONTENTS. 



414. The liviug coutcuts of young aud active cells are maiuly protoplasm 

 with water or watery sap which this has imbibed. Old and effete cells are 

 often empty of solid matter, coutaiiiiug ouly water with whatever may be 

 dissolved iu it, or air, accordiug to the tiuie aud circumstances. All the 

 various products which plants iu general elaborate, or which particular 

 plants specially elaborate, out of the common food which they derive from 

 the soil and the air, are contained in the cells, and in the cells they are 

 produced. 



415. Sap is a general name for the principal liquid contents, — Crude sap, 

 for that which the plant takes iu, Elaborated sap for what it has digested or 

 assimilated. They must be undistuiguishably mixed in the cells. 



416. Among the solid matters, into which cells convert some of their 

 elaborated sap two are general and most important. These are Chlorophyll 

 and Starch. 



417. Chlorophyll (meaning leaf-cj rpeti) is wliat gives the green color to 

 herbage. It consists of soft grains of rather complex nature, partly wax- 

 like, partly protoplasmic. Tiiese abound in the cells of all common leaves 

 and the green rind of plants, wherever exposed to the light. The green 

 color is seen through the transparent skin of the leaf aud the walls of the 

 containing cells. Chlorophyll is essential to ordinary assimilation iu plants : 

 by its means, under the influence of sunlight, tiie plant converts crude sap 

 into vegetable matter. 



418. Far the largest part of aU vegetal)le matter produced is that which 

 goes to build up the plant's fabric or cellular structure, either directly or 

 indirectly. There is no one good name for this most important product of 

 vegetation. In its final state of cell-walls, the permanent fabric of herb 

 aud shrub and tree, it is called Cellulose (408) : in its most soluble form 

 it is Sugar of one or anotlier kind ; in a less soluble form it is Dextrine, a 

 kind of liquefied starch -. iu the form of solid grains stored up in the cells 

 it is Starch. By a series of slight chemical changes (mainly a variation in 

 the water entering into the composition), one uf these forms is converted 

 into another. 



419. Starch {Farina or Fecula) is the form in which this common plant 

 material is, as it were, laid by for future use. It consists of solid grains, 

 somewhat different in form in different plants, in size varying from ^^ to 

 j-^ of an inch, partly translucent when wet, and of a pearly lustre. From 

 the concentric lines, which commonly appear under the microscope, the 

 grains seem to be made up of layer over layer. When loose they are com- 

 monly oval, as in potato-starch (Fig. 462) : when much compacted the 

 grains may become angular (Fig. 463). 



420. The starch in a potato was produced in the foliage. In the soluble 

 form of dextrine, or that of sugar, it was conveyed through the cells of the 

 herbage and stalks to a subterranean shoot, and there stored up in the 



