Page:Popular Science Monthly Volume 25.djvu/71

Rh that whatever may be the contents of these round, oval, hexagonal, oblong, or otherwise regular and irregular cells, we can not cook and eat any whole vegetable, or slice of vegetable, without encountering a large quantity of cell-wall. It constitutes far more than half of the substance of most vegetables, and therefore demands prominent consideration. It exists in many forms with widely-differing physical properties, but with very little variation in chemical composition—so little, that in many chemical treatises cellular tissue, cellulose, lignin, and woody fiber are treated as chemically synonymous. Thus, Miller says: "Cellular tissue forms the groundwork of every plant, and when obtained in a pure state its composition is the same, whatever may have been the nature of the plants which furnished it, though it may vary greatly in appearance and physical characters; thus, it is loose and spongy in the succulent shoots of germinating seeds, and in the roots of plants, such as the turnip and the potato; it is porous and elastic in the pith of the rush and the elder; it is flexible and tenacious in the fibers of hemp and flax; it is compact in the branches and wood of growing trees; and becomes very hard and dense in the shells of the filbert, the peach, the cocoanut, and the Phytelephas or vegetable ivory."

Its composition in all these cases is that of a carbohydrate, i.e., carbon united with the elements of water, which, by-the-way, should not be confounded with a hydrocarbon, or compound of carbon with hydrogen simply, such as petroleum, fats, essential oils, and resins. There is, however, some little chemical difference between wooden tissue and the pure cellulose that we have in finely-carded cotton, in linen, and pure paper-pulp, such as is used in making the filtering-paper for chemical laboratories, which burns without leaving a weighable quantity of ash. The woody forms of cellular tissue owe their characteristic properties to an incrustation of lignin, which is often described as synonymous with cellulose, but is not so. It is composed of carbon, oxygen, and hydrogen, like cellulose, but the hydrogen is in excess of the proportion required to form water by combination with the oxygen.

My own view of the composition of this incrustation (lignin properly so called) is that it consists of a carbohydrate united with a hydrocarbon, the latter having a resinous character; but whether the hydrocarbon is chemically combined with the carbohydrate (the resin with the cellulose), or whether the resin only mechanically envelops and indurates the cellulose I will not venture to decide, though I incline to the latter view. As we shall presently see, this view of the constitution of the indurated forms of cellular tissue has an important practical bearing upon my present subject. To indicate this beforehand I will put it grossly as opening the question of whether a very advanced refinement of scientific cookery may or may not enable us to convert nut-shells, wood-shavings, and sawdust into wholesome and digestible