322 



GENERAL SCIENCE 



Roots serve to hold plants in an upright position and 

 also to take food from the soil by the process of osmosis. 

 When two fluids are separated by a porous membrane they 





FIG. 281. Development of the 

 Bean. 



Note how the seed is pushed out 

 of the ground, the formation of the 

 seed leaves, and the withering of 

 the seed when the leaves and roots 

 are sufficiently developed. 



intermingle or diffuse, the greater flow 

 being toward the denser medium. The 

 fluid in the root hairs is more dense than 

 the soil water ; therefore the soil water 

 bearing plant food flows into the roots 

 faster than the sap flows out, and the 

 excess fluid is forced up into the plant. 

 This action takes place most rapidly 

 near the ends of the roots where the 

 root hairs are most numerous. A root F .}?- 282 ;77 A 



Seedling of the Castor 

 hair IS really a living plant Cell With Bean, Three Weeks Old. 



a wall so thin that water readily passes s '' s , te ; r > , ro ? ts ; c ' 



J expanded seed leaves; 



through into the interior Of the root, p, permanent leaves. 



Root hairs are long, hairlike structures almost colorless 

 in appearance (Figure 284). They are probably not 



