SIGNIFICANCE OF LIPOIDS 51 



From this it appears that lecithin is formed during germination ; 

 although there is, during the early stages of germination, a 

 diminution in the quantity present. It was found when once 

 the maximum was reached that this amount remained constant 

 until the whole of the endosperm was used up. 



The products of the decomposition of lecithin, viz. a fatty 

 acid, glycerophosphoric acid, and choline, have been detected by 

 Green and Jackson in the endosperm of germinating seeds of 

 Ricinus, and they suppose that the action is reversible, so that 

 the lecithin is formed by the combination of the products of 

 decomposition of the oil and protein reserves of the seeds. 

 Thus the oil provides the fatty acid and the glycerol, of which 

 the latter combines with phosphorus, obtained from the 

 aleurone grains, to form glycerophosphoric acid. The choline 

 is provided by the decomposition of the proteins by means of 

 a tryptic enzyme. But however this may be, in view of our 

 ignorance of these substances, and the fact that vegetable 

 lecithins apparently have seldom or never been obtained in a 

 state of purity, and the uncertainty relating to some of their 

 cleavage products, it does not appear profitable further to 

 consider here the theories which have been advanced to 

 explain their formation. 



Physiological Significance. 



Nothing of a very definite nature is known of the physio- 

 logical significance of the lipoids. Overton points out that 

 under certain condition's lecithin and similar substances have 

 the power of absorbing water, and suggests that the ectoplasm 

 may consist of layers of these substances which thus play an 

 important rdle in absorption and secretion. Green and Jackson 

 also consider that it exercises considerable influence on the 

 transport of materials from cell to cell. This view of the 

 lipoid nature of the plasmatic membrane is greatly supported 

 by the work of Czapek * on the surface tension of the external 

 limiting layer of the protoplasm. 



Lipoids may of course represent an intermediate product 

 between the fats and proteins, for it is a well-known fact that 



* Czapek : " Ueber eine Methode zur direkten Bestimmung der Oberflachen- 

 spannung der Plasmahaut von Pflanzenzellen," Jena, 1912. 



4* 



