136 VEGETABLE LIFE AND GROWTH. [SECTION 16. 



§ 2. CELL-CONTENTS. 



414. The living coutents of young and active cells arc mainly protoplasm 

 with water or waicry sap whicli this has imbibed. Old and effete cells are 

 ol"ten empty of solid matter, contaiuiug only water with wliatever may bo 

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

 various products which plauts in general elaborate, or which particular 

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

 tlie soil and the air, arc contained in the cells, and iu 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 undistinguisli:d)ly mixed in the cells. 



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

 elaborated sap two are geuei-al and most important. These are Chlorophyll 

 and Starch. 



417. Chlorophyll (meaning leaf-r/ reeii) 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 tlie 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 plauts : 

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

 into vegetable matter. 



418. Far the largest part of all vegetable matter produced is that which 

 goes to build up the ])lanl'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 

 and shrub and tree, it is called Cellulose (40S) : 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 : iu the form of solid grains stored np 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 oy 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 ditferent plants, in size varying from ^-^ to 

 5^'g-o of an inch, partly translucent when wet, and of a pearly lustre. From 

 the concentric lines, which commoidy appear inider the microscope, the 

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

 monly oval, as in potato-starch (Fig. 4G2) : when much compacted the 

 grains may become angular (Fig. 468). 



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

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

 herbage and stalks to a subterranean shout, and there stored up iu tlic 



