COMPARED WITH THOSE OP ANIMALS. 48 



nutrient fluid or organizable matter to the cells of the 

 parenchyma, which are the true vegetable laboratories. 

 Endosmosis and capillarity will account for the ascent of 

 the fluid in plants, and its distribution to the remotest parts 

 of the organism ; but when the fluid enters the cell-labo- 

 ratories of the parenchyma, its constituents are transmuted 

 into an immense variety of products by processes which 

 have hitherto totally eluded the researches of science. 

 Some of these products, such as chlorophyl, starch, gum, 

 sugar, and raphideSj-are elaborated more or less by the 

 cells of all plants ; others are restricted to certain species, 

 as for instance, the different varieties of endochrome, or- 

 ganic acids, resins, gums, alkaloids, fixed and volatile oils. 

 In many instances there is no apparent difference in the 

 form of the cells, which are closely united, forming part of 

 the same parenchyma ; and yet the diversity of their pro- 

 ducts proves that they are not the same cells. Thus we 

 have cells which secrete oils, resins, and different varieties 

 of endochrome in the midst of chlorophyl-secreting cells ; 

 in proof of which we refer the reader to the oil-cells which 

 ' produce the punctated appearance in the leaves of the 

 orange, to the resinous dotted foliage of Eupatorium 

 rotundifolium, and to the dark purple spots on the leaves 

 of Euphorbia maculata. Now since it is a well known 

 maxim in physiology that nothing constant is unimportant, 

 because experience and observation both prove that every- 

 thing constant is connected with the discharge of some es- 

 sential function of the organism, and as these plants never 

 grow without a manifestation of these peculiarities ; there 

 can be no doubt whatever that these cells which produce 

 them have a special and distinct work assigned, that they 

 are organically different from those cells which secrete the 

 chlorophyl, and that they are separate co-laborers in the 



