198 A TEXT-BOOK OF BOTANY. 



Abrin, occurring in the seeds of Abrus precatorius; Curcin, in the 

 seeds of Jatropha Curcas; Crotin, in the seeds of Croton Eluteria; 

 and Robin, in the bark of Robinia Pseud-acacia. The pollen 

 of rye is also said to contain a toxalbumin, which, when adminis- 

 tered in extremely small doses, accentuates the symptoms of hay 

 fever in patients afflicted with this disease. Under the name of 

 " Vegetable Agglutinins " have been brought those protein sub- 

 stances which when added to a suspension of blood-corpuscles rap- 

 idly cause them to agglutinate. Those substances that possess 

 the same properties but are not poisonous are known as 

 *; 'Phasins." (Consult "The Vegetable Proteins," by Osborne; 

 and." Beitrage zur Kenntnis der vegetabilischen Hamagglutinine," 

 by R. Robert.) 



ORIGIN AND FORMATION OF PLANT PROTEINS. It has been 

 shown that carbohydrates originate in chloroplastids and are 

 formed under the influence of sunlight from two simple substances, 

 viz., carbon dioxide and water. Protein substances, on the other 

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

 plasmic 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. Proteins arise through 

 the interaction of nitrates, sulphates, and compounds of ammonia 

 with either formaldehyde or some simple carbohydrate. It is 

 supposed that the nitrates and sulphates are decomposed 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 compounds the nitrogen is 

 supplied by hydrocyanic acid. Apart from the facts just men- 

 tioned, 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 



