Fats and oils are widely distributed in plants. They occur very commonly in the reproductive organs, both spores and seeds, as reserve food material. In fungi, oils are often found in the spores, but sometimes also in sclerotia, mycelia, or filaments. For example, the sclerotia of ergot have been found to contain as much as 60 per cent of oil. In higher plants, many seeds contain high percentages of oil, so as to make them commercial sources for edible or lubricating oils, such as olive oil, rape-seed oil, cottonseed oil, castor oil, corn oil, sunflower-seed oil, etc., etc. Nuts often contain large proportions of oil, the kernel of the Brazil nut, for example, sometimes contains as high as 70 per cent of oil, while an oil content of 50 per cent, or more, is common in almonds, walnuts, etc. Oils also occur as reserve food material in other storage organs of plants, such as the tubers of certain flowering plants, and the roots of many species of orchids. Sometimes the appearance of oils in the stems of trees, or the winter leaves of evergreens, seems to be only temporary and to occur only during periods of very low temperatures. Much less frequently, fats or oils are found in the vegetative organs of plants, as in the leaves of evergreens. Their appearance and functions in these organs seem to be much less certain than in the other cases cited above; although in rare cases a considerable proportion of oily material has been found to exist in definite association with the chloroplasts. The vegetable fats and oils have many important industrial uses. Some of them, such as olive oil, cottonseed oil, cocoanut oil, etc., are largely used as human food. Others, as castor oil, are used as lubricants. The so-called "drying oils" (see page 132), such as linseed oil, etc., are used in the manufacture of paints and varnishes. Some cheap vegetable oils are used as the basis for the manufacture of soaps, etc. Hence, industrial plants and processes for the extraction of oils from plant tissues are of very great economic importance. CHEMICAL CONSTITUTION The fats (of either plant or animal origin) are glycerides, i.e., glycerol esters of organic acids. As has been pointed out, esters are derived from organic acids and alcohols in exactly the same way that mineral salts are derived from inorganic acids and metallic bases. -------- Thus, Na|OH + H|ONO_2(HNO_{3}) = NaNO_{3} + H_{2}O -------- Base Acid Salt ----------- and, C_{2}H_{5}|OH + H|OOC·H = C_{2}H_{5}OOC·H + H_{2}O ----------- Alcohol Acid Ester --------------- or, R·|OH + H|OOC·R = R·OOC·R + H_{2}O --------------- Any alcohol Any acid Any ester