The Manufacture of Food 



29 



How the suppUes are obtained. Every industrial workshop 

 must constantly be provided with the raw materials needed 

 in the manufacture of its prod- 

 uct. Likewise the leaf must be 

 supplied with the substances 

 that it uses in the making of 

 food. These necessary supplies 

 come to the leaf through the 

 veins and the stomata. The 

 water passes into the leaf 

 through the water-conducting 

 tissue of the veins. The supply 

 of carbon dioxid reaches the 

 cells of the mesophyll through 

 the stomata and the intercel- 

 lular spaces. When the stomata 

 are closed, very little carbon 

 dioxid can enter, and at such 

 times the process of photosyn- 

 thesis is of necessity greatly 

 retarded. 



How the products and wastes 

 are removed. The manufac- 

 ture of carbohydrates in the 

 leaf goes on only during the 

 hours of sunlight ; the removal 



of food goes on at all times. The food-conducting tissue of 

 the veins furnishes the outlet for the product, which is trans- 

 ferred in the form of sugar. During the day the rate of 

 manufacture is so much greater than the rate of removal 

 of food, that starch and sugar accumulate. During the 



Fig. 18. Experiment to show the giv- 

 ing off of oxygen from a water plant 

 (Elodea) during photosynthesis. 



