OILS AND FATS 49 



Oils or fats form another important group of reserve-sub- 

 stances found especially in those seeds in which carbohydrates 

 are either scanty or absent (e.g. Castor Oil, Sunflower, etc.). 

 Drops of oil are, however, not uncommon in the ordinary vege- 

 tative cells, and are particularly abundant in some lower plants 

 [e.g. in the Alga Vaucheria (cf . p. 208) , and in the Ergot (Claviceps)] . 

 The vegetable fats are compounds (esters) of glycerine with 

 various fatty acids (palmitic acid, oleic acid, etc.), and are de- 

 composed by ferments known as Upases into these two con- 

 stituents. In most cases they occur as fluids within the plant, 

 although the fat of the Cocoa (Theobroma cacao), the so-called 

 Cocoa-butter, forms an exception to this. 



The oil appears in the cell-sap or protoplasm as shining 

 globular drops of varying size which are readily soluble in ether, 

 benzene, etc. ; some are even soluble in alcohol (e.g. those in the 

 seeds of the Castor Oil). When a considerable quantity of fat 

 is present (e.g. in the Brazil-nut), it can be squeezed out by 

 pressure on to a piece of filter-paper, producing a greasy mark. 

 The oil-globules turn pink or red on treatment with Scharlach 

 Red (Appendix II), and assume a blackish colouration with 

 osmic acid, which, however, also stains proteins and tannins in 

 the same way. If sections of oil-containing material be placed 

 in a solution of concentrated potash and ammonia in equal pro- 

 portions, the globules after some time lose their sharply defined 

 outline, and often become replaced by needle-shaped crystals. 

 The change, spoken of as saponification, is due to the breaking 

 up of the oil into glycerine and the fatty acid, the latter uniting 

 with the alkali to form the corresponding salt. 



Many plant-fats are of considerable economic importance ; 

 thus, olive oil is obtained from the fleshy fruit-wall of the Olive 

 (Olea euwpcza, mainly cultivated in the Mediterranean region) ; 

 coconut oil, used in the preparation of margarine, from the 

 ripe seeds of the Coconut Palm (Cocos nucifera) * ; and Castor 

 Oil from the seeds of the Castor Oil plant (Ricinus communis). 

 Other important commercial sources are Linseed (Linum usita- 

 tissimum), Cotton-seed (Gossypium spp.), Pea-nuts (Arachis 

 hypog<za,with. 38-50 per cent, of oil), and Soja-beans (Glycine spp.). 

 In most cases the oil is extracted after crushing, the ultimate 



1 Copra is the commercial name for the dried kernel of the Coconut. 



4 



