the walk, at the end of that time, stood in puddles, and the sap still bubbled np 

 through the gravel. On examining the roots with an ordinary microscope, the 

 discharge will be found to proceed from the whole of the exposed cells through 

 the section, and bubbles of air are frequently formed on the cut surface, evidently 

 showing that some kind of gas was present, either in the sap or in the cells. 



Such cases are doubtless much more common than is supposed. The sunflower, 

 bulk for bulk, imbibes and perspires seventeen more times fresh liquor than a 

 man, every twenty-four hours. A tree may be assumed to be a combination of 

 hollow tubes, freely communicating with each other, and inclosed in a skin through 

 which fluids ai'e capable of being absorbed on the one hand, and expelled on the 

 other. If we conceive a body of this kind, in which the tubes are nearly empty, 

 to have its lower extremity plunged in water, the absorbing power of the skin at 

 that part will begin to introduce the water into the interior, and this continuing 

 to go on for a sufficient time, the tubes must necessarily become at last filled with 

 water, rising up from below. To eifect this, no attracting force at the upper end 

 of the cylinder was necessary ; every particle of water which was absorbed by the 

 lower end having driven before it a corresponding volume of the water previously 

 existing in the apparatus. Under the influence of this operation, the tubes would 

 in time become full, and if unelastic, the introduction of more water would be 

 impossible. But if such tubes, and the skin that incloses them, were elastic and 

 extensible, then any such quantity of water might be introduced as the apparatus 

 could receive without bursting. If we, then, suppose that the one end of the 

 apparatus were cut open, the sides of the tubes would collapse, and the water 

 would be forced out till there was no more left than the tubes held in their ori- 

 ginal unstretched condition. A tree is just such an apparatus. Its tubes are 

 nearly empty at the fall of the leaf. During winter, the roots absorb water, and 

 fill the tubes again. By the arrival of spring, they are filled almost to bursting, 

 and then, if the stem is cut, it bleeds ; or, if the roots are cut, they bleed. 

 Bleeding ceases as the leaves unfold. The vine, the walnut, and the birch, are 

 all as incapable of bleeding as other trees, when their leaves are formed ; because 

 the leaves gradually empty the tubes, put an end to their distension, and prevent 

 its recurrence as long as they remain in an active state. 



The excessive loss of sap would not have taken place if the roots had been 

 wounded or cut in the summer or autumn. In the adjoining cut (Fig. 1) is 

 represented a tree ready for removal, with the rootlets carefully preserved from 

 injury, which should be done whenever practicable, but in practice these rootlets 

 are too often de- 

 stroyed ; and, in 

 that case, it would 



have been better ^^ 



to cut them ^^ 



while the tree had ^^ -vA ^ f h>\M ^ C^,,../:^^ 



its leaves on it -^^-^^^^^^^^^Illvi^JI^^XI^ 



the summer pre- 

 vious to the in- 

 tended removal. 

 There is no 

 period of the year 

 when the roots be- 

 come altogether 

 inactive, sayl'ro- 

 fessor Lindley 



