58 



COUESE OF THE SAP. 



PI. II. 



' the proper, constant, and inexhaustible sources of 

 oxygen gas ' ? 



Second In deciduous trees, and in the greater part of 



office of o -L 



mation rf"^' ^^g^^^^ evergrceus, if each leaf does not form a bud, 

 bud™*^"^" at least each leaf is accompanied by a bud. And I 

 imagine that one essential office of the leaf is the 

 formation and summer nutriment of the winter-hud. 

 Each bud forms a shoot, or a flower, or both, the next 

 year. This is the general rule. But vast quantities of 

 leaves fail to mature buds, vast quantities of buds fail 

 to produce shoots, and vast quantities of shoots fail to 

 grow. Wind, or an insect, or drought, or any thing 

 which injures or destroys a leaf, will injure or destroy 

 its bud, and consequently the next year's growth of 

 that bud. This is one chief cause of the baneful effect 

 of wind on trees. Besides this, the circulation of the 

 Third office sap is dependent on the leaf throughout the summer, 



of leaves, 



the Chang- as it Is dependent on the bud in the winter. The leaf 



ing of the 



the upward tum-tablc which shifts the sap from the up to 



the*^wiod, the down4ine in summer, as the bud is this turn-table 



downward lU the winter. Summer and winter this traffic is con- 

 conduit, . . , . . 



the bark, staut ; but as it IS less m winter, so the plant and staff 

 required to work it is less. Keep your turn-tables in 

 order, or lose your traffic. 



The growth That the growth in the girthing, or diameter of 



is f?oS\hf trees, is a downward growth, that is, from the descend- 

 downward 



peSdent^on ^^P' lesist that the descending sap is necessary 

 by exp^ri- growth iu girth, seems clear from this : If a 



ring of bark is taken off round a branch of a tree, so 



