198 A TEXT-BOOK OF BOTANY. 



The \^itamines. — A class of nitrogen compounds fCi^Hoo 

 O7N2), without which it is considered that no food is com- 

 plete. They were discovered in 1912 in the pericarp or husk 

 of rice. It has since been ascertained that they occur in the 

 majority of fresh animal and vegetable foods. The discovery has 

 marked an epoch in our understanding of such diseases as beri- 

 beri, which was supposed to be caused by a monotonous diet. It 

 was found that rice which is polished, i.e., deprived of the peri- 

 carp, has a tendency to induce beriberi and that the presence of 

 the husk makes it entirely wholesome. Funk discovered that 

 the pericarp of rice contained a necessary constituent of the 

 nerve tissue — a vitamine — for want of which the nerve fibers 

 deteriorated (Casimir P^unk, "Die Vitamine," 1914). 



Origin and Formation of Plant Proteins. — It has been 

 shown tliat carbohydrates originate in chloroplastids and are 

 formed under the influence of sunlight from two simple sub- 

 stances, viz., carbon dioxide and water. Protein substances, on 

 the other hand, are not formed in any definite organ, but arise in 

 the protoplasmic contents of the cell. This function is not limited 

 to the protoplasm of green plants, as fungi also possess this 

 property. Furthermore, proteins may be formed in organs 

 growing in the dark as well as those exposed to the light. Pro- 

 teins arise through the interaction of nitrates, sulphates, and com- 

 pounds of ammonia with either formaldehyde or some simple car- 

 bohydrate. It is supposed that the nitrates and sulphates are de- 

 composed by plant acids, furnishing the necessary nitrogen and 

 sulphur. Treub, by reason of his studies on Pangium edule, has 

 advanced the theory that in the construction of protein com- 

 pounds the nitrogen is supplied by hydrocyanic acid. Apart 

 from the facts just mentioned, all theories with regard to the 

 formation of proteins are mere speculations. 



We are indebted to Emil Fischer and his students (" Unter- 

 suchungen iiber Aminosauren Polypeptide und Proteine," Berlin, 

 1906) for much information concerning the structure of proteins. 

 They have prepared synthetically several protein-like substances, 

 although no natural occurring protein has as yet been obtained. 

 From these studies it has been shown that proteins belong to a 



