CONTENTS OF THE TISSUES. 57 



nutritive matter thus produced, and which all forming and vitally 

 active cells necessarily contain, namely the ternary (of which su- 

 gar and dextrine are representatives), and the quaternary (pro- 

 teine, protoplasm, &c.), have already been mentioned (27). 



80. Proper Juices, Caoutchouc, Essential Oils, Turpentines, &c, Of 

 the peculiar products of plants, which occur under an infinite va- 

 riety of forms in different species, it is only needful to say here, 

 that they doubtless arise from one or the other of the two classes 

 of assimilated matter just mentioned, by chemical transformations 

 which throw them out of the ranks of nutritive bodies. They seem 

 to be turned to no account in vegetable growth ; they undergo 

 changes on exposure to -the air, by which they become resins, 

 gums, wax, &c. ; they incline to extravasate into intercellular spa- 

 ces or into cavities of dead or effete tissues, or to be directly ex- 

 creted from the surface. So that we may regard them all, per- 

 haps, as of the nature of excretions, even where they are stored 

 up in the interior of the plant. For we must remember that the 

 vegetable has no organs or apparatus for eliminating arid casting 

 out excreted matters, except to a very limited extent by a few su- 

 perficial glands, which are found in some plants and in some 

 organs only. Caoutchouc exists in the form of minute globules, dif- 

 fused as an emulsion in the milky juice of plants, most abundantly 

 in Urticacece, Euphorbiaceas, and Apocynacea?. Gutta percha is 

 a similar product of the milky juice of a Sapotaceous plant. 



81. Starch (Farina, Fecula) is one of the most important and 

 universal of the contents of cells, in which it is often accumulated 

 in great quantity, so as to fill them completely (Fig. 52), as in 

 farinaceous roots, 



seeds, &c. It oc- 

 curs in the pa- 

 renchyma of al- 

 most every part 

 of the plant, ex- 

 cepting the epi- 

 dermis : but while chlorophyll is nearly restricted to the superfi- 

 cial parts, directly exposed to the light, starch is most abundant 



FIG. 51. Two cells of a potato, with some contained starch-grains, highly magnified; one 

 of the cells contains a few cubical crystals also. 



FIG. 52. A minute portion of Indian meal, strongly magnified; the cells absolutely filled 

 with grains of starch. 



