OBSERVATIONS UPON THE PHENOMENA OF PLANT-LIFE. 313 



pressed. It is evident, also that old trees on a clay hard-pan or any other un- 

 yielding subsoil must be thrown up by the process of growth. Every person is 

 familiar with the fact that large trees usually have the appearance of having 

 been thus raised, and their roots are often bare for a considerable distance 

 around the trunk. 



This lifting of the tree from its bed would seem to be advantageous to it by 

 tightening the roots so as to hold it tirmly in place, notwithstanding the possi- 

 ble elongation of their woody fibre by the tremendous strains to which they are 

 eubjected during violent storms. This method of securing the tree iu place 

 would be still further improved by the constant enlargement of the roots by 

 the annual deposition of a layer of wood, and the consequent filling of any 

 spaces formed in the soil by the movements of the roots, caused by the sway- 

 ing of the tree in the wind. 



This slight annual elevation of trees by the increase in diameter of their 

 horizontal roots furnishes an explanation for the differences of opinion in re- 

 gard to the question whether a given point on the trunk of a tree is raised in 

 the process of its growth. Whde it has been demonstrated by Prof. Asa Gray 

 that two points in a vertical line on the trunk of a tree will not separate as it 

 enlarges, it seems equally clear that both of them may be quite perceptibly 

 elevated in the course of time. 



It has been stated on good authority that, at Walton Hall, in England, a 

 mill-stone was to be seen, in 1863, in the ceotor of which was growing a filbert 

 tree, which had completely filled the hole in the stone, and actually raised it 

 from the ground. The tree was said to have been produced from a nut, which 

 was known to have germinated in 1812. The above story has been declared 

 false, because, as asserted, the tree could not have exerted any lifting power 

 upon the stone. It is, however, not difficult to see that it may be true, and is 

 even probable. 



Yet it should be remembered that the amount of elevation, in any cas« 

 where it occurs from the increase in the size of horizontal roots, must depend 

 upon the firmness of the material on which they rest, and can never exceed 

 one-half the diameter of the largest roots. When, therefore, a writer, as has 

 happened, asserts that, during a visit to Washington Irving at Sunnyside, he 

 carved his name upon the bark of a tree beneath which he was sitting in cou- 

 yersation with the illustrious author, aod that many years after he went to the 

 place, and with much difficulty discovt-red the identical inscription, high up 

 among the branches, far above his reach, it is altogether probable that bis feel- 

 ings were teo many and too exalted for the ordinary use of his intellectual 

 faculties. 



DR. PETTIGUEW'S HYPOTHESES EXPLODED. 



Since the publication of the paper on the'- Circulation of the Sap in Plants," 

 in the last volume of the Agriculture of Massachusetts, a course of lectures on 

 the '• Physiology of the Circulation in Plants, in the Lower Animals, and in 

 Man," by Dr. J. Bell Pettigrew, has been published by Macmilian & Co., of 

 London. The hypotheses adopted by this author are quite extraordinary, and 

 evidently announced without: ihe slightest attempt at demonstration, although 

 he has invented a new method of accounting for the phenomena of the mo- 

 tions of the sap. Thus he says, *' In trees the sap flows steadily upward in 

 spring, and steadily downward in autumn." Also, ''Much more sap is taken 

 up than is given off in spring, in order to administer to the growth of the 



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