WHERE ROOTS GROW 



9 



dry soil they are usually long. Roots of the willow run into 



wells and drains and into the margins of creeks and ponds. 



Roots may frequently cause trouble by 



clogging drain-pipes. Grow plants in a 



long, narrow box, in one end of which 



the earth is kept very dry and in the other 



moist: observe where the roots grow. 



28. The absorbing surface of the roots 

 is near their ends. As the roots become 

 old and hard, they serve only as channels 

 through which water and substances in 



solution pass, and as hold- 



fasts or supports for the 



plant. The root-hold of a 



plant is very stong. Slowly 



pull upwards on some plant, 



and note how firmly it is 



anchored in the earth. With 



the increase in diameter, the 



upper roots often protrude 



above the ground and be- 



come bracing buttresses. 



These buttresses are usu- 



ally largest in trees that 

 always have been exposed to strong winds. 

 (Fig. 10.) 



29. The Root-hairs. The larger part 

 of the water and mineral nutrients ab- 

 sorbed by the root is taken in through 

 root-hairs. (Fig. 11.) These are very del- 

 icate prolonged surface cells of the 

 roots. They are borne for a short dis- 

 tance just back of the tip of the root. 



30. The root-hairs are very small, 

 often invisible. They, and the young 



11. Root-hairs 

 of the radish. 



12. Aerial roots of 

 creeper or 



