AGRICULTURAL CHEMISTRY. 129 



well as in the food of animals, by effecting the transformation of cel- 

 lulose and starch into dextrin and sugar, and of pectose into pectin. 



In all plants, and in nearly all parts of plants, we find some fixed 

 oil, fat (or wax;) but it is chiefly in certain seeds that the} 7 occur 

 most abundantly. Thus the seeds of maize, oats, hemp, flax (fig. If), 

 colza, cotton, pea-nut, beech, almond, sunflower, &c, contain from 

 G to 70 per cent, of oil, which may be in great part removed by 

 pressure. In some plants, as the African palm and the Nicaraguan 

 tallow-tree, the oil is solid at ordinary temperatures, while many 

 plants yield small quantities of wax, which either coats their leaves 

 or forms a "bloom" upon their fruit. The oils differ exceedingly in 

 taste, odor, and consistency, as well as in their chemical composition. 

 They all contain much carbon, and less oxygen than is requisite to 

 form water with their hydrogen. 



The oil or fat of plants appears to be, in many cases, a product of 

 the transformation of starch or other member of the cellulose group, 

 for the oily seeds when immature contain starch, which vanishes as 

 they ripen, and in the sugar-cane the quantity of wax is always 

 largest when the sugar is least abundant, and vice versa. 



It has long been known that the brain and nervous tissue of ani- 

 mals contain several oils of which phosphorus is an essential ingredi- 

 ent. Recently Knop has discovered that the sugar-pea yields a sim- 

 ilar oil containing 1.25 per cent, of phosphorus, in addition to carbon, 

 hydrogen, and oxygen. 



The bodies to which attention has thus been briefly directed, con- 

 stitute by far the larger share of the solid matter not only of the 

 young cell but of all vegetation. They comprise, nearly all, those 

 vegetable substances which are employed as food or otherwise pos- 

 sess any considerable s^ricultural significance. The numberless acids, 

 alkaloids, resins, volatile oils, coloring matters, and other principles 

 existing in small quantity in the vegetable world, are unimportant to 

 our present purpose. 



We find under the microscope that certain of these bodies have an 

 organized structure; such are cellulose, starch, inulin, and gluten, 

 (aleuron of Hartig;) while others, as dextrin, gum, sugar, albumin, 

 and casein, are the products of the disorganization of those above 

 mentioned — the structureless materials, out of which the organized 

 portions of the plant renew themselves. 



To return to the cell. As the life of the plant progresses, not only 

 does the form of the cell greatly change in many cases, but it under- 

 goes very marked internal transformations. The liquid that fills the 

 young cell contains both dextrin and albumin ; from the former is 

 elaborated the walls of new cells, or else the existing cells are filled 

 up more or less completely with some solid carbo-hydrate resulting 

 from the transformation of dextrin. Thus in the potato tuber the 

 cells are almost entirety occupied with starch. In the stem of trees 

 the cells are lengthened and thickened by the continuous deposit of 

 cellulose with other ill-defined bodies, and the result is wood. In 

 the seeds of the cereal grains and numerous other plants we find the 

 cells densely crowded, (hence polyhedral in figure.) and filled with 

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