PROTEIN SYNTHESIS 87 



mulberry, the reserve carbohydrate is in the form of a 

 thick deposit on the inner surface of the cell wall. This 

 is a substance closely related to cellulose, one of the hemi- 

 celluloses. The sugars in fruits perhaps belong in the 

 category of stored foods although they serve rather as 

 a bait for animals which on eating the fruit aid in the 

 distribution of the seeds. 



128. The carbohydrates produced, whether first 

 stored up or used immediately, have for their ultimate 

 destination various functions. As building materials 

 they are used up in the formation of cell walls in the grow- 

 ing parts of plants. Whether they are thus used directly 

 or must first become a part of the protoplasm is uncertain. 

 The use of carbohydrates in furnishing energy to the 

 plant will be discussed under the topic Respiration. 



129. A considerable portion of the carbohydrates 

 eventually becomes built up into those very complex 

 nitrogenous compounds called proteins. Whether the 

 carbohydrates are taken as such and combined with 

 nitrogen obtained from the nitrates and sulphur and 

 phosphorus from the sulphates and phosphates re- 

 spectively, the product being proteins, or whether as 

 seems possibly may be the case part of them are broken 

 down and then combined with the nitrogen to form 

 hydrocyanic acid (HCN) this being polymerized and 

 combined with other carbohydrate molecules and with 

 sulphur and phosphorus, is not known. In any case 

 hydrocyanic acid is often formed in plants in which active 

 protein production is taking place. 



130. Certain bacteria, chiefly parasitic in the roots 

 of plants of the bean family (Fabaceae), are capable, 

 when supplied with carbohydrates and the necessary 

 mineral salts, of using the atmospheric nitrogen (as dis- 

 solved in the soil water) in building up protein com- 



