13S VEGETABLE LIFE AND GROWTH. [SECTION 16, 



§ 2. CELL-CONTENTS. 



414. The living contents of young and active cells are mainly protoplasm 

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

 often empty of solid matter, containing only water with wliatever may be 

 dissolved in it, or air, according to the time and circumstances. All the 

 various products which plants in 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 in, Elaborated sap for what it has digested or 

 assimilated. They must be undistinguishably 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-green) is what gives the green color to 

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

 like, partly protoplasmic. These 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 and the walls of the 

 containing cells. Chlorophyll is essential to ordinary assimilation in plants ; 

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

 into vegetable matter. 



418. Par the largest part of all vegetable 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 iinal state of cell-walls, the permanent fabric of herb 

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

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

 kind of liquefied starch : in 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 of 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 -5^ to 

 j^jljni of an inch, partly translucent when wet, and of a pearly lustre. Prom 

 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 tto 



