68 FOOD FROM THE SOIL 



needed must come in as long as the land can furnish them 

 in soluble form. Absorption was illustrated before by an 

 artificial arrangement because the root -hairs are so small 

 that they cannot be seen readily. But all parts of the 

 root can absorb some water. 



142. Fleshy pieces of root or stem will absorb water 

 from weak solutions and become rigid ; in strong solutions 

 such fleshy parts will give up their water and become flexi- 

 ble. To experiment further with this principle of absorp- 

 tion, cut several slices of potato tuber about one -eighth of 

 an inch in thickness, and let them lie in the air half an 

 hour. Place a few of these slices in some of the strong 

 fertilizer solution I. Place similar pieces in the weak 

 solution II. In half an hour or more, those pieces in the 

 weak solution will be very rigid or stiff (turgid). They 

 will not bend readily when held lengthwise between the 

 fingers. Compare these slices with those in the strong 

 solution, where they are very flexible (flaccid). This 

 bending is evidently due to the fact that those in the 

 strong brine have actually lost some of their water. So 

 the potato tuber could take in soil water con- 

 taining a small amount of food ; but if the 

 water contained much food material the potato 

 would actually lose some of the water which 

 it held. 



143. These experiments not only demonstrate 

 how the roots absorb water containing plant- 

 food, but they emphasize the fact that the out- 

 **side solution must be very dilute in order that 

 water may be absorbed at all. The root-hairs ab- 

 too strong sor ^ wa f er w Jii c h has dissolved only a small amount 



food solu- 

 tion, of plant -food from the richness of the soil, and 



not from such rich solutions as the sap of the plant itself. 



]44. The plant may be wilted, and even Mlled by at- 

 tempting to feed it food solutions which are too strong. 



