THE WORK OF ROOTS 121 



passes through the root-han* and the soft outer part 

 (rind or cortex) of the root to the woody strands 

 in the center (shown in the figure as four groups of 

 thick-walled cells), and by means of these up into the 

 stem. (The four groups of thin -walled tissues alter- 

 nating with the wood are the bast; in the center, 

 surrounded by the wood and bast, is the pith.) 



Do the root-hairs attach themselves closely to the 

 particles? Place some well- soaked seeds (Radish seed is 

 especially good) on the surface of fine, moist gravel in 

 a pan; over this lay a piece of glass to retain moisture. 

 In two or three days the roots will be covered by a 

 thick felt of glistening, white root-hairs. As they come 

 into contact with the particles of gravel they become 

 firmly attached to them. When this has happened, 

 lift the seeds; are the attached particles lifted with 

 them; how large a pebble can be lifted in this way; 

 when the pieces are too large to be lifted does the 

 root -hair loosen its hold or does it break, leaving a 

 portion attached to the particle ? What conclusion do 

 you draw as to the closeness and firmness of the 

 attachment ? 



In dry soil the water exists in the form of innumer- 

 able little reservoirs, which must be tapped by the 

 root -hairs. To remove the water some force must bo 

 used, for the water adheres quite firmly to the soil- 

 particles. Not only must the reservoir be tapped but 

 the water must be drawn forciblv from it. How does 



