ORGANIC SUBSTANCES AS PLANT FOOD 215 



It is not known in just what way the coordination of the work 

 of the enzymes is brought about in the living cell. There are sup- 

 posed to be present certain so-called antiferments, which may stop 

 the activity of certain enzymes; and coferments, which hasten it. 

 In the living cell substances may also be found of the nature of 

 proferments, which are not active themselves, but which can 

 easily be changed into enzymes. Enzymes therefore are, as 

 Palladin figuratively expressed it, the "day laborers" of the proto- 

 plasm, produced by it and set to work according to its need, 

 and then inhibited or destroyed when there is no need for their 

 action. 



Besides hydrolysis, enzymes also bring about other more com- 

 plex reactions, such as oxidation and reduction of organic sub- 

 stances. These reactions will be discussed in the next chapter. 



69. Fats and Their Utilization in Germination. Lipoids and 

 Phosphatides. Organic Acids. — Fats and oils are found in almost 

 all seeds. They enter into the composition of the protoplasm of 

 embryonic cells. But in most seeds they are found in considerable 

 quantity as reserves readily available in germination. 



Fats, as is known, are complex esters of glycerine and fatty 

 acids either of the saturated or of the unsaturated series having the 

 general formulae C„H 2n 2 , C„H 2 „-202, C n H 2n _ 4 2 . Saturated 

 acids, such as stearic and palmitic, give solid fats, while unsat- 

 urated, as oleic, linoleic and linolenic, are mostly liquid fats. 

 Natural oils, found in seeds, are composed mostly of a mixture of 

 different fats. In this connection it is of interest to note that in 

 plants of a warm climate fats with a higher melting point predom- 

 inate, as, for example, in the oil of cacao, cocoanut, and other 

 tropical products; while in plants of a temperate zone, such as 

 hemp, flax, poppy, and others, liquid or unsaturated fats pre- 

 dominate. Unsaturated fats are easily oxidized in the air, usually 

 forming a hard film on the surface, hence, they are called drying 

 oils and are used in the manufacture of oil paints. Through the 

 action of alkalies and acids, fats are easily hydrolyzed even at low 

 temperatures, adding 3 molecules of water and breaking up into 

 glycerine and a fatty acid. The hydrolysis of palmitin, for instance, 

 proceeds according to the following formula : 



C 3 H 5 (Ci C H 3 i0 2 )3 + 3H 2 -> C 3 H 5 (OH) 3 + 3Ci 6 H 32 2 . 



Palmitic Glycerine Palmitic acid 



