ABSORPTION, DIFFUSION, OSMOSE. 



19 



w 



39. Absorption by root hairs. — If we examine seedlings, 

 which have been grown in a gerniinator or in the folds of paper 

 or cloths so that the roots will be free front particles of soil, we 

 see near the growing point of the roots that the surface is 

 covered with numerous slender, delicate, thread- 

 like bodies, the root hairs. Let us place a por- 

 tion of a small root containing some of these 

 root hairs in water on a glass slip, and prepare it 

 for examination with the microscope. We see 

 that each thread, or root hair, is a continuous 

 tube, or in other words it is a single cell which 

 has become very much elongated. The proto- 

 plasmic membrane lines the wall, and strands of 

 protoplasm extend across at irregular intervals, the 

 interspaces being occupied by the cell-sap. 



We should now draw under the cover glass 

 some of the five per cent salt solution. The 

 protoplasmic membrane moves away from the cell 

 wall at certain points, showing that plasmolysis is 

 taking place, that is, the diffusion current is out- 

 ward so that the cell-sap loses some of its water, 

 and the pressure from the outside moves the 

 membrane inward. We should not allow the salt 

 solution to work 011 the root hairs long. It should 

 be very soon removed by drawing in fresh water 

 before the protoplasmic membrane has been 

 broken at intervals, as is 



Fig. 26, 



apt to be the case by the 



strong diffusion current 



and the consequent 



strong pressure from 



without 



of protoplasm now moves 



outward as the diffusion current is inward, and soon regains its 



former position next the inner side of the cell wall. The 



foot hairs then, like other parts of the plant which we have 



T^T^.1. vt^^T^KT-on^ Seedling of radish, showing root treatment -wdth 



inememorane ^^j^^^ salt solution 



Fig. 27. 

 Root hair of com 

 before and after 

 5< 



