134 PLANTS AND MAN 



There is no chemical difference between fats and oils; it is 

 common practice to refer to those which are solid at ordinary 

 temperatures as fats, and to those which are liquid at the same 

 temperatures as oils. Fats are comparatively rare in plants while 

 oils are very common. Oils are generally lighter than water and 

 insoluble in it. Fats and oils are synthesized from carbohydrates 

 through intermediate compounds such as fatty acids and 

 glycerol; these are transformed into the more complex fats and 

 oils by the activity of the enzyme lipase. Two common fatty 

 acids produced by plants are formic acid, found in nettles, and 

 acetic acid, found in vinegar. The oil first appears as droplets or 

 vacuoles scattered through the cytoplasm of the cell. In a few 

 plants, the oils are secreted by special plastids — the elaiop lasts 

 — ^which bear the same relation to fat formation as the leuco- 

 plasts do to starch production. Elaioplasts are particularly 

 numerous in the vanilla plant and some composites. The chief 

 commercial source of plant oils is from seeds; in this plant organ 

 the amounts of oil vary from 4% in corn to 30% in flax, 54% in 

 cocoa and 65% in coconuts. Familiar oils include castor oil, 

 coconut oil, olive oil, palm oil, cottonseed oil and linseed oil. 



The most common of the fats produced by plants are the 

 WAXES — compounds resulting from the union of a fatty acid and 

 a complex alcohol. They form the "blooms" found on leaves and 

 fruits, which act as impervious coatings and prevent the loss 

 of water from underlying tissues. Some plants, such as rhodo- 

 dendrons and magnolias, have very glossy leaves due to the 

 abundance of wax formed on their surface. The bloom on a 

 fruit, such as a grape or plum, is also of value in checking fungus 

 attacks. This waxy covering prevents the rot-producing fungi 

 from gaining entrance into the succulent fruit tissues. Straw- 

 berries picked early in the morning, for example, while this wax 

 coat is firm and intact, rot less than those picked in late afternoon 

 when the wax has been softened and rendered less effective by 

 the heat of the sun. 



Protein Foods 



Photosynthetic glucose contains within itself all the elements 

 — secured from air and water — necessary for forming all the 



