216 TEXTBOOK OF PLANT PHYSIOLOGY 



This process is known as "saponification." It is applied in 

 industry in the manufacture of soap and glycerine. 



As reserve substances, fats have a number of important advan- 

 tages over carbohydrates. Being insoluble in water, they readily 

 become inert reserve substances, thus entirely disappearing from 

 the sphere of other reactions and processes going on in the cell. 

 Being liquids, they can completely fill the tissues of reserve organs. 

 Moreover, they do not contain hygroscopic water, of which 15 to 20 

 per cent is present in reserve carbohydrates as a useless ballast in 

 dry seeds. Finally, they contain very little oxygen, and conse- 

 quently upon oxidation develop a large amount of heat energy per 

 unit weight. When 1 g. of fat is oxidized in the organism, or out- 

 side of it, there is obtained on the average 9.3 cal. of heat while 1 g. 

 of protein will give 5.7 cal. and 1 g. of starch only 4.1 cal. These 

 properties make oil an extremely valuable reserve substance, and 

 hence it is but natural that in 90 per cent of all plants the seeds 

 belong to the oily type. The only advantage possessed by reserve 

 carbohydrates lies in the fact that without any complex chemical 

 changes they can be converted into glucose and the monosacchar- 

 ides in general, substances of ready availability and great useful- 

 ness to plants, while fats must undergo many transformations 

 before they may be utilized. 



In the germination of oily seeds, the stored fat is used very 

 rapidly. Miintz observed that of 8.9 g. of fat found in 20 g. of 

 poppy seeds prior to their germination, after 2 days there was left 

 6.8 g. and after 4 days only 3.9 g. This consumption of oil is 

 preceded by its saponification, which may be seen from the fact 

 that the quantity of free fatty acids, which is quite negligible in 

 the seeds, grows very rapidly at germination. In the case of the 

 germinating poppy seeds only 10 per cent of the fat was composed 

 of free fatty acids before germination, but after 2 days this had 

 increased to 53 per cent, and after 4 days to 97 per cent, in other 

 words, almost half of the fat was already hydrolyzed. It was not 

 possible to demonstrate an accumulation of glycerine, as it very 

 quickly undergoes further changes. 



The saponification of fats in germinating seeds is brought 

 about by special enzymes, known under the general name of 

 lipases. Lipase is easily obtained by grinding with glycerine 

 germinating castor beans. It will rapidly hydrolyze fats into 

 glycerine and fatty acids. Since the rate of the reaction is con- 



