ORGANIC SUBSTANCES AS PLANT FOOD 219 



instantaneous formation of a great number of small calcium oxalate 

 crystals in the protoplasm, when it is under the influence of ultra- 

 violet rays, has been observed by Nadson. In all probability, this 

 is connected with the rapid disintegration of the compound protein 

 substances of the protoplasm. 



70. Reserve Proteins and Products of Their Hydrolytic 

 Decomposition. — The nitrogenous reserve substances of plants 

 are represented almost exclusively by proteins. This group of 

 compounds is of an extremely complex composition, consisting of 

 at least five elements: carbon, oxygen, hydrogen, nitrogen, and 

 sulphur, and often phosphorus as well. Nitrogen constitutes 

 15 to 19 per cent of the protein molecule. In many respects, 

 protein substances are analogous to polysaccharides. They are 

 represented by large molecules, of a definitely colloidal character, 

 and they are comparatively easily hydrolyzed into more simple, 

 easily crystallizable products, which belong to the group of amino 

 acids; hence, the protein molecule must be considered as consisting 

 of a number of amino acids joined to each other through the 

 process of dehydration, just as we think of the starch or cellulose 

 molecule as being composed of molecules of glucose united to each 

 other. The essential difference, however, is that in splitting poly- 

 saccharides only one or two monosaccharides are formed, while at 

 least ten or more amino acids enter into the building of the protein 

 molecule. Owing to this complex composition, the protein group 

 is much larger than that of polysaccharides. 



For a long time protein substances were regarded as charac- 

 teristic integral parts of living matter. It was supposed that in 

 them was to be found the riddle of life. Therefore, the possibility 

 of synthesizing proteins was considered almost akin to the pos- 

 sibility of artificially creating a living organism. At the present 

 time, proteins are not viewed in this light. To be sure, these sub- 

 stances are still considered as absolutely necessary for the creation 

 of the living protoplasm ; however, they are no more necessary than 

 are the lipoids or carbohydrates. The protein nature of enzymes, 

 for some time considered quite probable, is now refuted by the 

 majority of investigators. For a long period, there prevailed the 

 theory of the extreme lability of the protein molecule, i.e., that in 

 the course of the life processes it must necessarily be broken down 

 and built anew. But at the present time, this theory also has 

 been abandoned. 



