30 



MORPHOLOGY OF ROOTS. 



[LESSON 5. 



imbibe. Accordingly, as long as the plant grows above ground, and 

 expands fresh foliage, from which moisture much of the time largely 

 escapes into the air, so long it continues to extend and multiply its 

 roots in the soil beneath, renewing and increasing the fresh surface 

 fof absorbing moisture, in proportion to the demand from above. 

 And when growth ceases above ground, and the leaves die and fallf 

 or no longer act, then the roots generally stop growing, and theif 

 soft and tender tips harden. From this period, therefore, until 

 growth begins anew the next spring, is the best time for transplant- 

 ing ; especially for trees and shrubs, and herbs so large that they 

 cannot well be removed without injuring the roots very mnch. 



68. We see, on considering a moment, that an herb or a tree 

 consists of two great surfaces, with a narrow part or trunk between 

 them, one surface spread out in the air, and the other in the soil. 

 These two surfaces bear a certain proportion to each other ; and the 

 upper di'aws largely on the lower for 

 moisture. Now, when the leaves fall 

 from the tree in autumn, the vast sur- 

 face exposed to the air is reduced to a 

 very small part of what it was before ; 

 and the remainder, being covered with 

 a firm bark, cannot lose much by evap- 

 oration. In common herbs the whole 

 surface above ground perishes in au- 

 tumn ; and many of the rootlets die at 

 the same time, or soon afterwards. 

 So that the living vegetable is reduced 

 for the time to the smallest compass, 

 to the thousandth or hundred-thou- 

 sandth part of what it was shortly 

 before, and what remains alive rests 

 in a dormant state, and may now be 

 transplanted without much danger of 

 harm. If any should doubt whether 

 there is so great a difference between 

 the summer and the winter size of 

 56 plants, let them compare a lily-bulb 



with the full-grown Lily, or calculate the surface of foliage which 



PIG. 55. Seedling Mapl, of the natural size, showing the root-hairs. 56. A bit of ttM 

 nd of the root magnified. 



