CHAPTER IX 



ABSORPTION AND OSMOSIS 



Vocabulary 



Gravitation, the attraction of the earth which draws everything 



downward. 



Successive, one after another. 

 Aerial, living in the air, as applied to roots. 

 Hydrotropism, the response of plant parts to water. 

 Geotropism, the response of plant parts to gravitation. 

 Osmosis, the diffusion of two liquids or gases through a membrane, 



the greater flow being toward the denser substance. 

 Turgescence, the support of plant parts, especially leaves, due to 



the presence of water in the tissues. 



The preceding chapter should have given us a rather definite 

 idea as to the structure of roots, and the names, at least, of some 

 of their functions. 



This chapter deals with absorption, the most important function 

 of all, since it is one of the principal ways in which plants obtain 

 food materials. We shall study in detail the adaptations of the 

 root for this fundamental function. 



Necessity of Water for Plants. All living matter depends more 

 or less on liquids of various sorts, and the plant, like the animal, 

 has its circulating fluids, bearing nourishment and removing 

 waste, storing food, and supplying oxygen to convert that food 

 into living energy. 



From the delicious juices that flavor the peach and sweeten 

 in the heart of the sugar cane, to the bitter milk that flows in the 

 dandelion or lures the unwary to death in the poisonous mush- 

 room, all consist largely of water, absorbed from the soil by the 

 action of the roots. 



This absorbed water is of threefold value to the plant. It 

 supplies a very necessary portion of the plant's food, as water 



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