270 THE MAINTENANCE OF THE INDIVIDUAL 



of sugar in the leaf, we find oxygen is given off as a by-product. 

 The reaction may be expressed by the following formula : 



6 CO2 + 6 H2O + energy from sunlight = CeHi^Oe + 6 O2 



(glucose) 



The value of this reaction to mankind is obvious. The by-product 

 oxygen, which is poured into the air by green plants, is used by 

 animals as well as plants in their respiratory processes. This exchange 

 of oxygen and carbon dioxide by plants and animals gives us one of 

 the most significant and far-reaching interrelationships seen in the 

 organic world. 



Briefly summing up the process of food making in plants we find 

 that raw materials pass in the form of water and soil solutes from 

 the soil through the root hairs and up the vascular bundles of xylem 

 into the leaf, where water is taken into the individual green cells. 

 Carbon dioxide reaches the cells from the air through the stomata 

 and to a lesser extent probably *in the water stream through the roots. 

 In sunlight, the process of photo.synthesis takes place. Elaborated 

 foods made in the form of sugars may be changed by enzymes to 

 starches and immediately stored in the leaf, or may be passed down 

 through the sieve tubes of the phloem to various parts of the plant 

 where they may be used or stored. Fats are probably synthesized 

 from carbohydrates in the green parts of plants, while proteins seem 

 to be formed in the cells irrespective of the presence of chlorophyll. 

 Enzymes play a very important role both in the manufacture and 

 in the use of food and are essential to respiration and oxidation. The 

 digestive processes which go on in the leaf and other cells of the plant 

 are also due to enzymes. 



All that has been said in the preceding pages leads to the most 

 important plant function, the reproduction of the species. With 

 vegetative propagation by means of budding, runners, underground 

 stems, tubers, or some of the other asexual means of continuing life, 

 plants would not go far. To establish outposts in far-flung dominions 

 they must have means of travel. These can only be obtained through 

 free moving parts. Such plants are seeds and fruits, which may be 

 dispersed by outside agencies far from the parent plant. 



The life of the flowering plant culminates in the production of seeds 

 and fruits. As growth progresses and food is accumulated, a time 

 comes, sooner or later, when the energies of the plant are directed to 

 the rapid production of the reproductive organs. Often this growth 



