WORK OF LEAVES: ASSIMILATION 10$ 



about 185 grams dry substance. This included other things than 

 starch. Brown and Morris * estimate that in one day (twelve 

 hours) one square meter of leaf surface of the sunflower will 

 make about 8 grams of carbohydrates of which the larger part is 

 sugar, the smaller part starch. This would make, on the same 

 estimates as above, about 15-20 grams of carbohydrate as the 

 result of one day's work of a vigorous sunflower on a warm, 

 bright day. 



175. Amount of C0 2 use(f during photosynthesis. Large 

 quantities of CO 2 are used in photosynthesis. A sunflower plant 

 uses about 50 grams CO 2 per day (= nearly 2 oz.). Supposing 

 the earth were covered with sunflowers it has been estimated that 

 they would consume 135,000,000,000 kilograms (= 297,000,000,- 

 ooo Ibs.). The amount of CO 2 in the air, if not replenished, at 

 this rate would last the sunflowers about twenty months. This 

 estimate is perhaps excessive. Another estimate is that a hectare 

 (2^ acres) of forest would consume 11,000 kg. (= 24,200 Ibs.) 

 CO 2 per year. This large amount of CO 2 is being continually 

 restored to the air by the burning of wood, coal, etc., for food, and 

 by the respiration of animals so that the normal balance is main- 

 tained. The celebrated Krupp works for the manufacture of 

 ordnance at Essen, Germany, alone produces about 2,500,000 kg. 

 (= 5,500,000 Ibs.) CO 2 per day. It is estimated that the human 

 beings of the earth give back to the air about 12,000,000 kg. 

 (26,400,000 Ibs.) CO 2 each day.f 



III. ASSIMILATION. 



176. The term assimilation usually has a wider applica- 

 tion by students of plants than by students of animals. 



Assimilation in animals is the building up of new living matter 

 and structures of the body, while in plants it has been customary 

 to use the word assimilation not only for the building up of new 

 living substance and new structures of the organism, but also for 



* Journal Chem. Soc., 63 (Transact.), 604. See Jost, Pflanzenphysiolo- 

 gie, 140, 1904; p. 114, Engl. Ed., 1907. 



t See "Text Book of Botany," Strasburger, Noll, etc., 196, English 

 edition. 



