understand how the countless little root-hairs act, — each one like 

 the tube A', if only the whole surface of the tube A' were a blad- 

 der membrane, or something acting similiarly ! The soil water 

 does not contain much of the land's fertility ; that is, it is a very 

 weak solution. The active little root hair, on the other hand, is 

 alwa^'s filled with cell sap, a more concentrated solution ; hence 

 soil water must come in, and along with it come also small quan- 

 tities of dissolved fertilizers. 



7. The plant absorbs fertilizer solutions as lo7ig as they are used 

 for the growth of the pla^it. — The fertilizers (salts) which are dis- 

 solved in the soil water also diffuse themselves through the 

 membrane of the root-hairs, each ingredient tending indepen- 

 denth' to become as abundant inside the root-hair as outside in 

 the soil water. Now once inside the root-hair, these absorbed 

 fertilizer solutions pass on to root and stem and leaf to be utilized 

 in grow^th. As long as the}^ are used up, however, more must 

 come into the root-hairs, in order to restore the equilibrium. 

 Thus those substances which are needed must come in as long as 

 the land can furnish them in soluble form. 



8. Fleshy pieces of root or stern will absorb zvater from weak solu- 

 tions and become rigid ; in strong solutions such fleshy parts will 

 give 2ip their water and become flexible. — We have illustrated 

 absorption b}' an artificial arrangement because the root-hairs 

 are so small that they cannot be seen readil3\ But all parts of 

 the root, even the fleshy part, can absorb some water ; and 

 to experiment further with this principle of absorption, we cut 

 several slices of potato tuber about one-eighth of an inch in 

 thickness, and let them lie in the air half an hour. Put a few of 

 these slices into some of the strong fertilizer .solution I., such as 

 was used in A', Fig. 3. Put other similar pieces into some of 

 the very weak solution II. In about half an hour or more we 

 find that those pieces in the weak solution are 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 the)- 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 containing a small amount of food ; but put in 



