How Plants Draw in Various Materials 



M 



through the stems to the leaves, as sho^vn very clearly in the con- 

 ventionalized plant of figure 54, A. Outside of the ducts lie some 

 rows of rounded-elongated cortical 

 cells, each of which retains its lining 

 of protoplasm and is shown by tests 

 to contain a solution of sugar. Finally, 

 outside of all lies the single thin line 

 of epidermal cells, which display a 

 very striking feature, viz., a great 

 many are prolonged into slender cy- 

 lindrical closed tubes, which are ob- 

 viously identical with the root hairs al- 

 ready observed in the young living 

 roots; and each hair is lined by living 

 protoplasm and, as shown by suitable 

 tests, contains a solution of sugar. 

 Now the structures important from 

 the view of water-absorption are the 

 ducts, the cortical cells, and the root 

 hairs; and these parts constitute the 

 water-absorbing machine. And this 

 machine, if reduced to a single cell of 

 each kind, would be constructed some- 

 what as suggested by figure 55. 



We turn now to the forces con- 

 cerned in absorption. Most people, 

 if questioned, would doubtless express 

 the belief that roots suck up water in 

 much the same manner that a wick 

 sucks up oil, that is, by the power, 

 called in physics capillarity, — the same 

 which takes liquids up fine tubes. In- 

 deed this was once the belief of botanists themselves, as witnessed 

 by their former use of the term "spongiole, " that is "little 



Fig. 55. — A diagram of the con- 

 struction of the water-absorbing 

 machine, as it would appear if 

 reduced to a single root hair, 

 cortical cell, and duct. Pro- 

 toplasm is shaded; circles are 

 water; crosses are sugar; the ar- 

 rows show direction of move- 

 ment. Magnification as in Fig. 6. 



