PRINCIPLES OF THE GROWTH OF TREES. il 



next spring the bud grows, forms a shoot, and the two por- 

 tions become securely united by the new wood. Unless the 

 cambium is vigorous enough to join the wood to the stock, 

 the operation cannot succeed ; and this is the reason why, with 

 vigorously growing stocks, in which the sap is flowing freely, 

 which are consequently rapidly forming new wood, budding 

 succeeds better than with feeble growers, where but little of 

 this natural cement exists. 



The rapidity with which leaves exhale moisture is shown 

 by severing them from the stem in dry weather. They soon 

 wither and become dry. Cut a shoot from a tree, and throw 

 it down in the sun's rays, and it will quickly shrivel, in con- 

 sequence of the rapid escape of its moisture through the 

 leaves. But first cut off all the leaves, and the shoot will re- 

 main plump a long time. This is the reason that it becomes 

 necessary to remove the leaves at once from scions cut for 

 budding. 



Hence also the reason that plants and trees are so liable to 

 die if transplanted with the leaves on, a disaster which may 

 be partially prevented in trees by removing the leaves; and 

 in plants or cuttings with leaves on, by covering them imme- 

 diately with a bell-glass which, by holding the watery vapor, 

 keeps a humid atmosphere about them. It is for this reason, 

 also, that when young trees lose a large portion of their roots, 

 a part of the top must be cut off, to prevent the heavy evap- 

 oration which all the leaves would occasion. 



A sunflower plant, about three feet high, was found to ex- 

 hale from its leaves in very dry weather between one and two 

 pints of water in a day. A bunch of growing grass placed be- 

 neath a cool inverted glass, soon covered the sides of the glass 

 with condensed drops from the vapor, and in a few minutes 

 the water ran down the sides. These experiments show the 

 great amount of water needed by growing plants; and also 

 prove the mistake which some persons commit, by leaving 

 weeds to grow to shade the ground and keep it moist, while 

 these weeds are actually pumping the water rapidly up from 

 the soil, and dissipating it through their leaves. 



The absolute necessity of leaves to the growth of a tree is 

 shown by the fact that when they are stripped off by cater- 

 pillars, the tree ceases to grow till new ones expand; and if 



