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- 
