THE CONVERSION OF THE PRODUCTS OF ASSIMILATION. II 



f59 



formula C.^Hj^Oj, the second, CJl^„_fi^, and the third, CJ^^^_fi^. To the first 

 group belong laurinic acid {C^^^fi^), myristic acid (Cj^HjgOg), palmitic acid 

 (CigHgjOj), stearic acid (CigHggOj), and arachidic acid (CgoH.^O,) ; to the second 

 series belong hypogaeic acid (CigHoy02), oleic acid (CigHg^Oj, and brassidic or 

 erucic acid {Q^^^f)^) ; to the last group, linoleic acid (CigH^gOj) (compare 

 Schmidt, 1891). [An enumeration of all the fats which occur in seeds will be 

 found in Czapek's Biochemie, I.] The glycerine esters of these fatty acids are 

 briefly described as palmitin, stearin, olein, &c., and they are to be considered 

 as formed from glycerine and a fatty acid by withdrawal of water, and con- 

 versely they may, by absorption of water, be decomposed into glycerine and 

 a fatty acid : — 



Palmitin Glycerine Palmitic acid. 



Such a decomposition, which we may obviously consider as a case of 

 hydrolysis, actually takes place in the course of germination. According to 

 R. H. Schmidt (1891), germinating seeds contain an appreciable quantity of 

 free fatty acid, amounting to from 10 per cent, to 30 per cent., and there can 

 be no doubt that its occurrence is due to the action of an enzyme, lipase. Green 

 (1890) extracted such an enzyme from seeds of Ricinns, and was able by its 

 means to obtain glycerine and a free fatty acid from castor oil apart altogether 

 from the seed. The presence of glycerine, however, has not hitherto been 

 demonstrated in the germinating seed, obviously because it rapidly undergoes 

 transformation and migrates easily from cell to cell. Fatty acids, imtil a short 

 time ago, appeared to be incapable of translocation from cell to cell ; the cell- 

 wall, saturated with water, was held to form an impassable barrier to any such 

 movement. According to R. H. Schmidt, this is perfectly true of artificial 

 cellulose walls, although not for the walls of living cells, which allow fats to 

 penetrate them in considerable quantity, more especially if the walls contain 

 a certain amount of free acid. It may be supposed that some substance present 

 in the cell-wall unites with the free fatty acid to form a soap, and that this 

 soap permeates the cell-wall and thus permits the fat to pass through. This 

 takes place all the more readily if the oil be subdivided into very minute 

 drops, that is to say, is emulsified, and the fatty acids are well known to have 

 an emulsifying power. 



In addition to Ricinus, several other seeds, such as those of rape, poppy, 

 and hemp, have been shown by Sigmund (1890-2) to contain a fat-splitting 

 enzyme, so that we have every right to assume the general distribution of 

 fatty oils and the corresponding frequency of lipase. More detailed investi- 

 gations on this subject are not as yet forthcoming, and we know still less as 

 to the process which microscopical research has established beyond a doubt 

 (Sachs, 1859), but which, from the purely chemical point of view, is incompre- 

 hensible, viz. the transformation of fats into sugar. The amount of sugar 

 present in germinating oily seeds renders it impossible that it has been 

 derived from glycerine only ; the fatty acids must obviously also contribute 

 to the formation of carbohydrates (compare Lecture XIV). 



In addition to non-nitrogenous we also meet with nitrogenous reserves 

 deposited in seeds in the form of froteid ; the relative proportion of nitro- 

 genous and non-nitrogenous substances is in the highest degree variable. 

 Whilst in general the non-nitrogenous substances are predominant, there are 

 many plants, more especially the Leguminosae, which contain a very large 

 percentage of nitrogenous reserves. A glance at the following table (Konig, 

 1882) demonstrates very effectively this variation : — 



Seed. Per cent, of nitrogenous substance in dry weight. 

 Rice (undecorticated) 6-49 



Wheat i4'3o 



Kidney beans ^*94 



Linseed 29>3a 



