X. THE CHEMICAL CONSTITUENTS OF PLANTS 199 



Phytosterol, C 26 H 43 OH, which closely resembles cholesterol found in 

 animals, occurs in the seeds of peas, beans and almonds, in wheat and 

 maize, and in many vegetable oils. It is a solid crystalline substance, 

 melting at 133 and soluble in hot alcohol, in ether, carbon disul- 

 phide, or chloroform. It is volatile. Its constitution is not under- 

 stood, but it probably is a monacid alcohol. ^ 



III. THE OEGANIC ACIDS AND THBIE SALTS. 



A large number of organic acids have been detected in various 

 vegetable products, occurring generally as potassium, sodium, or 

 calcium salts, though sometimes in the free state or in combination 

 with organic bases. Numerous acids have been detected in various 

 vegetables ; only a few typical ones can be considered here. The 

 organic acids are characterised by containing one or more " carboxyl " 

 groups, .COOH. 



The following may be taken as examples : 



Formic acid, H.COOH. 



Oxalic acid, COOH. COOH. 



Tartaric acid, COOH.CH(OH).CH(OH).COOH. 



Malic acid, COOH.CH(OH).CH 2 .COOH. 



Citric acid, CH 2 (COOH).C(OH)(COOH).CH 2 (COOH). 



Succinic acid, CH 2 (COOH).CH 2 (COOH). 



Fumaric acid, CH(COOH):CH(COOH). 



For the properties, methods of preparation, and constitution of 

 these acids the reader is referred to any modern textbook on organic 

 chemistry. The free acids themselves often occur in plants, particu- 

 larly in fruits, e.g., malic acid, occurring in apples, mountain-ash 

 berries, gooseberries, red currants, blackberries and sour or morella 

 cherries. 



In other cases, acid potassium or calcium salts are the cause of 

 the acidity, e.g., potassium hydrogen tartrate in grapes, acid potassium 

 malate in sweet cherries. In many fruits several organic acids or 

 their salts occur in association, e.g., gooseberries, currants and 

 cherries contain both malic and citric acids, while mountain-ash 

 berries and tamarinds contain malic, citric and tartaric acids. 



Oxalates of potassium and, particularly, of calcium are extremely 

 widely distributed in the vegetable kingdom, the latter occurring often 

 in the solid, crystalline state in the cells of plants. The crystals of 

 the calcium salt have the composition CaC 2 4 .3H 2 O and are soluble in 

 saccharine solutions. Acid potassium oxalates, KHC 2 O 4 and KHC 2 O 4 

 + H 2 C 2 O 4 , occur in solution in the sap of certain plants, e.g., sorrel, 

 rhubarb. 



Tannic acid or tannin is very abundantly distributed in the vege- 

 table .kingdom. It varies in composition and properties according to 

 its origin. 



Tannin was formerly looked upon as a glucoside, but the tannic 

 acid, its chief constituent, was looked upon as an anhydro-acid. 1 



1 Schiff, Ann., 170, 43. 



