ABSORPTION 143 



impelling the movements, and involving three phases: (a) First 

 entrance of substances into the organism, or absorption; (b) 

 removal from one part of the plant to another, or transport; and 

 (c) removal from the plant, or elimination. 



Of all substances absorbed by plants the most obvious and 

 abundant is water, which, therefore, may best be considered 

 first. The water-absorbing structures of the higher plants are 

 the young roots with their hairs, of which the student should 

 now review his knowledge (by aid of new microscopical studies 

 upon germinator-grown material if necessary) until he under- 

 stands fully, and can diagram clearly, the structure and connec- 

 tions of tip, hairs, cortex, and vascular system, both as to walls 

 and protoplasm, and he should inform himself upon the com- 

 position of the cell sap in these various parts. The study will 

 show plainly enough that the absorption of water is through 

 solid walls which are without openings even when viewed under 

 the highest powers of the microscope. Faced thus by a ques- 

 tion of physics, the wise course for the student is to ask of 

 that science whether any process is known whereby liquids are 

 absorbed through imperforate membranes. And an answer is 

 ready. Such absorption can occur through osmosis, which is 

 a process involving a solution of some diffusible substance 

 separated from the water by an imbibition membrane. With 

 these matters the student must now make himself well acquainted, 

 in part through study of the proper literature, but in part through 

 personal contact with the phenomena, which he can best bring 

 clearly before him in the form of this problem: 



What are the actual phenomena, and the physical explana- 

 tions of diffusion and imbibition? 



Experiment. Fill with water an erect test-tube or equivalent, 

 and stand it in a solid place of even temperature. Drop quickly to 

 the bottom a lump of solid fuchsin, and observe the movement of the 

 color, distinguishing convection and other movements from that of 

 diffusion Also, replace the fuchsin by some colored solution, poured 

 through a thistle-tube to the bottom. 



Experiment, (a) Suspend a strip of membrane (page 146) and 

 a strip of filter-paper each of the same measured dimensions, such as 

 5X2 cm , with one end in water, and observe the comparative rate of 



