1 68 PLANT LIFE. 



chlorophyll bodies, but is probably a transformation product 

 from a sugar, to which it is closely akin chemically. 



234. 2. Proteids. — The formation of proteids is even 

 more obscure. Apparently at some point in the series of 

 changes following the formation of formaldehyde, molecules 

 of nitrogen are added to form an amid. Amids, especially 

 asparagin, leucin, and tyrosin, are common in plants. They 

 may also be produced by the use of carbon, hydrogen, and 

 oxygen from complex carbohydrates by katabolism (^j 238). 

 They are soluble in water, crystallizable, and, hence, can be 

 carried by osmosis from cell to cell. From these, by the 

 addition of sulfur and phosphorus, proteids are formed, but 

 neither the steps in the process nor its conditions are well 

 understood. Apparently the formation of amids occurs in 

 green tissues and under the influence of light. It is probable 

 that even among the green plants the formation of proteids 

 takes place in other parts than the green tissues, as it is 

 certain that this occurs also among the colorless plants. The 

 proteids which are built up from the amids are used directly 

 in the repair of protoplasm. Since carbohydrates are neces- 

 sary to the formation of proteids, and since they can be 

 manufactured only by the green plants under the influence of 

 light, it will be seen how essential these plants are for the 

 world's food supply. 



E. Storage and translocation of food. 



235. Storage and transfer. — Both in the colorless and 

 green plants it is necessary that the foods made or absorbed 

 should be transferred from one point to another where they 

 are to be used. The larger the plant, the more important 

 does this transfer become. In many plants, also, it is 

 desirable that a supply of reserve food be stored for use when 

 a supply is no longer available from the outside or by 

 manufacture. 



