OF LIVING FORMS; OR, MORPHOLOGY. 105 



grows by insinuating itself, cell by cell, through 

 the interstices of the soil, winding and twisting 

 whithersoever the obstacles in its path determine, 

 and growing there most, where the nutritive materials 

 are added to it most abundantly. As we look on 

 the roots of a mighty tree, it appears to us as if 

 they had thrust themselves with giant violence into 

 the solid earth. But it is not so; they were led 

 on gently, cell added to cell, softly as the dews 

 descended and the loosened earth made way. Once 

 formed, indeed, they expand with an enormous 

 power, and it is probable that this expansion of the 

 roots already formed may crack the surrounding 

 soil, and help to make the interstices into which 

 the new rootlets grow. Nor is there any good 

 reason for assuming that the roots encounter from 

 the soil a greater resistance to their growth than 

 the portions of the stem meet with from other causes. 

 We must not forget the hard external covering 

 of the parts exposed to air and light. In some 

 classes of palms this resistance is so great that the 

 growth of the tree is stopped by it. 



Similar to the case of the root are those in which 



