X. 



THE CHEMICAL CONSTITUENTS OF PLANTS 



211 



The usual method of estimating proteids in analysis is by deter- 

 mining the amount of nitrogen present, and then assuming that this 

 nitrogen constitutes about 16 per cent of the weight of the albuminoids. 

 The percentage of nitrogen found is therefore multiplied by 6-25, 

 and the product is given as the percentage of albuminoids. This 

 only gives approximate values, since all proteids do not contain exactly 

 16 per cent of nitrogen. The following table gives the percentage of 

 nitrogen found in various proteids and the factor which, multiplied by 

 the percentage of nitrogen found, will give the amount of albuminoid 

 present l : 



(ii) The Simpler Amino-Compounds. Under this heading may 

 be conveniently grouped together those substances which were for- 

 merly classed as Amides. They are compounds of much less com- 

 plexity than the proteids and are, for the most part, to be regarded as 

 derivatives of ammonia, NH 3 , by the replacement of one atom of 

 hydrogen by an organic radicle. 



They include many of the amino-acids already mentioned as pro- 

 ducts of the hydrolysis of proteids. 



The simpler amino-compounds occur widely distributed in the 

 vegetable kingdom, being especially abundant in immature plants. In 

 many cases, they are transition compounds formed in the synthesis of 

 the proteids. Being soluble in water and diffusible, they can readily 

 pass through the cell walls of plants, which is not the case with the 

 colloidal proteids. Hence they permit of the transference of nitrogen- 

 ous matter from one part of a plant to another. In all processes in- 

 volving such translocation, these simpler amino-compounds ai e formed 

 by the hydrolysing action of enzymes upon the proteids, to be fol- 

 lowed by the re-formation of the latter in the new locality. Hence 

 the simpler amino-compounds are to be most readily detected in 

 plant tissues during germination and during seed formation. They 

 are products of both katabolism and anabolism. A few of the more 

 common of these compounds may be briefly described and may be 

 .taken as types of many others that have been found in plants. 



1. Asjiaragine, which is really amino-succinamic acid, 



Wiley, Agric. Analysis, Vol. Ill, p. 445. 



