818 THE ROLE OF NITROGEN, ETC., I., 



4. Nucleic acid, a product of the hydrolysis of nuclein in cell- 

 protoplasm and nuclei was isolated from plant-seeds first by 

 Osborne and Harris. (52) The nucleic acids are glucosides, and 

 yield on hydrolysis a pentose sugar, purin bases, pyrimidin bases 

 and phosphoric acid; these vary with the different sources. From 

 the resting embryos of wheat the above authors separated 3*5%. 

 of tritico-nucleic acid; they also noticed that, in meal which had 

 been stored for some time, the nucleic acid had disappeared. The 

 hydrolytic products were identified as amino-purins — guanin and 

 adenin, resembling the animal nucleic acids; but the pyrimidin 

 base was represented b}- uracil (dioxy-pyrimidin), while in that 

 from animal sources it is usually thymin or a mixture of thymin^ 

 cytosin and uracil (one, two, or all three); on the other hand, 

 thymin has not yet been obtained from plant nucleic acids. 



Since the pyrimidin structure is contained likewise in the 

 purins it has long been discussed whether the former do not owe 

 their origin to a cleavage of the purins during hydrolysis, 



N = CH N = CH 



I 1 

 HO C-NH ^ 



I I 

 HC CH 



ll ll OH 



II II 



N-C-N ' 



N-CH 



The nucleic acids combined with protein form the most essential 

 part of all germ-cells, and the presence of a carbohydrate group 

 in these is of peculiar interest. Most of our recent knowledge of 

 the nucleic acids we owe to the classic researches of Levene. 



Vernin is another peculiar body, also possessing the constitu- 

 tion of a purin-glucoside, discovered by Schulze(53) in 1886, in 

 Lupinus a/bus, and so named by him. He found it in 

 various species of Lupinus, Vicia, and clover, from the aqueous 

 extracts of which it was precipitated by mercuric nitrate. To 

 this substance Schulze has ascribed the formula C 1G H 20 N 8 O 8 ; 

 and, after hydrolysing it by boiling with acid, he obtained as 

 cleavage-products guanin and a pentose sugar(54). The amount 

 of vernin present in lupin seeds is very small, being about 0025%. 



