52 



Elementary Plant Physiology. 



extensions of the epidermal -cells of the roots, are to be seen. 

 Cut a thin cross-section of one of the roots. Observe the rela- 

 tion of the root-hairs to the underlying parenchymatous tissues. 

 Note also the open tubes and vessels to be seen in the center 



of the root. Take up seedlings 

 grown in soil, and note the adhe- 

 sion of soil particles to the root- 

 hairs. 



The walls of root-hairs consist 

 of cellulose, much like parchment, 

 through which liquids pass by 

 osmose in the same manner as 

 through the parchment walls of the 

 dialyzer. The root-hair, however, 

 contains protoplasm, a thin layer 

 of which lines the wall and forms 

 a second membrane with qualities 

 different from those of the outer 

 wall. Furthermore, the qualities of 

 the living membrane may be 

 changed by the protoplasm, and are 

 under its control at all times. 

 All substances do not pass through 

 both membranes with equal rapid- 

 ity, and some may penetrate one 

 and not the other, giving rise to 

 the phenomena of plasmolysis. 



47. Plasmolysis. — Place 

 some filaments of Spirogyra or a 

 bit of epidermis with root-hairs in 

 water, on a slide, and examine with a magnification of 400 to 

 600 diameters. Now, with a bit of blotting paper, draw off 

 the water from one side of the cover glass, and add a drop 

 or two of a 5 per cent, solution of common salt at the opposite 



Fig. 2g. — Seedlings of mustard. 

 A, witii particles of soil cling- 

 ing to root-hairs ; B^ after re- 

 moval of soil by a stream of 

 water. After Sachs. 



