144 



CONSTRUCTION OF PLANT'S FOOD 



construction diffuses into the intercellular spaces, and into them 

 water also evaporates from the cell-sap. This stream of 

 activities is none the less real because noiseless and unseen by 

 the eye. 



a B C D E b F 



FIG. 75. Diagram to show the effect of different portions of the spectrum on photo- 

 synthesis, o, to F, different regions of the spectrum from red to blue. A filamentous alga 

 lies across these, and bacteria are collecting about the alga, with greatest frequency in the 

 red between B and C, indicating the greatest evolution of oxygen there. (After Pfeffer.) 



The steps in the chemical process of food-construction can- 

 not be followed, but it is interesting to note how simple the 

 process might be, as, for example, 6CO 2 + 6H 2 O = C 6 H 12 O 6 

 (glucose) + 6O 2 . 



Epidermis 

 FIG. 76. Diagram to show the three general tissue regions of a leaf. 



Relation of Leaf as a Whole to Photosynthesis. A leaf 

 from the standpoint of its cellular anatomy consists of three 

 distinct parts: the epidermis, the ground or fundamental paren- 

 chyma, and the vascular bundles (Fig. 76). The epidermis 



