THE LIVING PLANT 



23 



The dense solution also passes through the membrane into 

 the weaker solution as can be noticed by the sweet taste of 

 the water in the beaker, but most of the passage is from the 



weaker to the stronger concentrated _____ __ 



solution. The passage of solutions 

 of different densities through semi- 

 permeable membranes into other 

 solutions in this way is known as 

 osmosis. The root-hairs are able to 

 take up water and substances in 

 solution because the cell-sap is of Ceff Wa// 

 greater concentration than the solu- 

 tions in the soil. But if the solu- 

 tions in the soil should become 

 stronger than the cell-sap in the 

 root-hairs, the cell-sap would move 

 outward into the soil solutions, and 

 injury or death to the plant would 

 be the final result. This is one 

 reason why plants cannot grow in 

 soils strongly alkaline. 



Before the salts taken up by root-hairs can be used by the 

 plant, they must be transported through the roots and stem 

 to the leaves where they are manufactured into plant-foods. 

 It is important to understand that the older roots do not 

 absorb solutions, but carry them. 



Roots also serve as storehouses for food materials, most of 

 which are in the form of starches-. Thick fleshy roots possess 

 a large amount of stored food. Plants living two years 

 (biennials) usually do not produce seed the first year, but 

 manufacture and store up food in the roots. The stored food 

 is used the second year to aid in producing the top of the plant, 

 and the thick roots shrivel. The plant produces seed the 

 second year and then dies, root and top. Carrots, parsnips, 

 and the like, are examples. 



Nucleus 



FIG. 10 Root-hair magnified. 



