42 PHENOMENA OF PLANT-LIFE. 



the scar and made the grafting complete. The structure will 

 be understood by examining figure 38. 



But the grafting of roots is still more common and curious. 

 They seem to cohere without the least difficulty, especially 

 those of the white pine, which is doubtless owing to the soft- 

 ness of the bark and young wood, and the fact that they grow 

 so nearly at the same level in the earth. A specimen from 

 the vicinity of the College, exhibiting a large number of grafts, 

 is represented in figure 39. 



A branch of gray birch, which has united with its own trunk 

 by an attachment formed in the angle of another branch above 

 it, is shown in figure 40. 



The rootward flow of elaborated sap is well illustrated in a 

 specimen of aspen in the College museum, around which is 

 twined a vine of bittersweet. (Figs. 41-42.) 



From the observations above made, it will be seen that there 

 is no difficulty in accounting for the curious fact which has 

 long been regarded as a great mystery, that the stumps of fir 

 trees, which do not sprout, have been known to continue 

 forming new layers of wood and bark for a great number of 

 years. Dutrochet mentions the case of a stump of the silver 

 fir which thus grew from 1743 till 1836, when it was still 

 alive, having formed, since the tree was felled, ninety-two thin 

 layers of wood. The roots of the living stump were doubt- 

 less grafted to the roots of some healthy tree or trees in its 

 vicinity, and their elaborated sap was attracted into the sound 

 bark and supplied the necessary material for the development 

 of new tissues under the influence of its vital force. The 

 outer layer of the roots of the stump was thus renewed an- 

 nually, and so they retained their power of absorption ; but 

 since the top of the stump, becoming dry and having no 

 foliage, could not exhale moisture, the crude sap of its roots 

 ascended into the neighboring tree or trees to which they 

 were united. Thus a sort of circulation was maintained 

 sufficient to explain the phenomena observed. 



Another peculiarity often to be seen in the stems and 

 branches of trees and shrubs, as in the pear, the apple, the 

 hemlock, and the lilac, is the spiral growth or twisting of the 

 wood and bark, which is sometimes visible during the life of 

 such specimens, and alwa} 7 s when the bark is removed and the 



