COMPARISON OF STARCH MAKING AND MILLING 83 



taken in through the stomata and reaches the green cells by way 

 of the intercellular spaces and by diffusion from cell to cell. Water 

 reaches the green cells through the veins. It then passes into the 

 cells and there becomes part of the cell sap. The light of the sun 

 easily penetrates the cells of the palisade layer, giving the energy 

 needed to make the starch. This whole process is a very delicate 

 one, and will take place only when external conditions are favor able « 



Air 



Food 



Compare the work of this part of a leaf (in starch making) with that of a mill. 



For example, too much heat or too little heat stops starch making 

 in the leaf. This building up of starch, with the release of oxy- 

 gen by the chloroplasts in the presence of sunlight, is called yho- 

 tosyn'thesis} 



Manufacture of Fats. — Inasmuch as tiny droplets of oil (or fat) 

 are found inside the chlorophyll bodies in the leaf, we believe that 

 fats, too, are made there, probably by a transformation of the 

 starch already manufactured. 



Protein Making and its Relation to the Making of Living Mat- 

 ter. — Protein is a part of the food which is necessary to form 



^ The process of photosynthesis is very complicated. It probably consists of 

 three steps : first, the taking in of the raw materials, COo and H2O ; second, the rear- 

 rangement of the elements within the green cells ; and third, the formation of 

 very simple sugars, then of more complex sugars, and finally of starch. The 

 process appears to be under the control of enzymes of different kinds, which cause 

 these progressive changes to take place. Enzymes also change the sugars, which 

 are carried to other parts of the plant for storage, into insoluble starch. 



