ADJUSTMENT TO WATER 



67 



times behaving as though each had an incUviduahty of its own. 

 In the cLassical experiments of Hales (1727), the maximum 

 transpiration of a sunflower was found to be 850 gm. in a twelve- 

 hour day, and 85 gm. at night. Sachs found also in the sun- 

 flower that the leaf surface lost water about half as rajjidly as 

 it evaporates from a water surface under the same conditions. 



lli'l >l Ml 



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j^*>!5AHi*Jar 



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Fig. 19. A battery of potometers for the ready comparison of the water 

 loss of plants of the same or different habitats. 



According to Wiesner, the Indian corn loses per hour for each 

 square decimeter of leaf surface 785 mg. in sunlight. 114 mg. 

 in diffuse light, and 97 mg. in darkness, while one of the woody 

 mallows (Malva arborea) loses respectively 70, 28, and 23 mg. 

 It has been found that a plant of Indian corn transpires 14 kg. 

 of water during its period of growth (173 days), and a hemp plant 

 27 kg. in a growing period of 140 days. Haberlandt has esti- 

 mated that the oat plants covering one hectare lost more than 

 2,000,000 kg. during their period of growth, while a similar num- 

 ber of barley plants transpired more than 1,000, 000 kg. The 

 transpiration of a large tree reaches an enormous total during 

 one summer. Von Hohnel has estimated that a booch tree tran- 



