CH. V, 4] 



ABSORPTION BY ROOTS 



225 



progress in plants, such reactions rarely occurring except 

 in solution. Fifth, it provides a medium of transport, 

 in form of solution, for substances through the plant. Sixth, 

 It is "needed to compensate the incessant loss by transpira- 

 tion. These are the 

 reasons why plants 

 must have plenty of 

 water. 



The water used by 

 ordinary plants is 

 wholly absorbed 

 through their roots, 

 and none is taken 

 through leaves or 

 stems. Further, the 

 actual absorption is 

 known to take place 

 in the young parts of 

 roots, and mainly 

 through the root hairs. 

 The hairs are thus 

 effective, not through 

 any special power de- 

 nied to other cells of 

 the young root, but 

 simply through the 

 great surface they 

 spread. It is because 

 these hairs, tightly 

 adherent to the soil, 

 are mostly torn away FIG 166 _ A plan of a root ag an absorbing 



when roots are lifted mechanism, arranged as in Figs. 11 and 105, 



from thp <sni1 that with similar si S ns for water, protoplasm, and 

 )m the SOU, that gugar A t the tip the growing point ; at the 



plants Commonly wilt left, pith ; a duct ; two rows of cortex ; the root 



rm trfmQrklantinfr nnrl hairs. Note that hairs and cortex contain 



m &> d [ protoplasm and sugar, but the duct contains 



recover only after neither. 



