Vegetable Physiology — Circulation of the Sap. 31 



If the leaves of a peach tree are stripped off, the fruit amounts to nothing. 

 This fact was exempUfied twice in Kansas during the last decade by the grass- 

 hopper invasion of that period. When the leaves of the grape or the goose- 

 berry have been devoured by caterpillars, the fruit remains small and sour, 

 and entirely worthless for the food of man. If any healthy tree be persist- 

 ently defoliated during the growing season, the tree will die. These facts 

 led early botanists to form the opinion that leaves were merely "a clothing, 

 or protection against colds and heats." Though this ancient theory is cer- 

 tainly true to a certain extent, still it is only a very small portion of the func- 

 tions of the leaves. For it is in the leaves that those changes are effected by 

 which the juices of the plant, relieved from the water — which is unnecessary 

 for the functions of life — are rendered fitting for the nourishment and growth 

 of the plant. 



That leaves exhale moisture is proved also by the simple experiment of 

 gathering the leafy branch of a tree, and immediately stopping the wound 

 at its base with wax, or some other fit substance, to prevent the effusion of 

 moisture in that direction. In a very short time the leaves droop, wither, 

 and fade. If the branch in this condition be placed in a very damp cellar, 

 or immersed in water, the leaves revive and assume their original appear- 

 ance. This experiment also shows their power of absorption. 



The chief office of the stem api^ears to be to elevate the leaves, the flowers 

 and the fruit into the most favorable position for receiving the influence^! 

 light, heat and air, for it is upon these that their full development depends. 

 But this is not its only function ; in combination with the roots and leaves 

 (nature's wonderful laboratory) the crude sap, in its ascent, is divested of its 

 rawness and aqueous matter and converted into nutritious sap, capable not 

 only of supplying to the different parts of the structure the materials neces- 

 sary for the maintenance of their healthfulness, for the repair of injuries, and 

 for the production of entirely new parts, but also of furnishing the ingredi- 

 ents of those several products which the various tribes of plants may be said 

 almost to create from the elements around them, and which are so valuable 

 to man as articles of diet, as medicines or as articles of use in his various 

 manufactures. All these varied substances originate in the ascending sap in 

 its passage through the sap wood {alburnum) and flowing sap {cambium laner) 

 by the exhaling process, in which the leaves play the most conspicuous part, 

 for by them it is concentrated by the loss of its water not only into solid mat- 

 ter, but into those secretions which almost every tribe of j^lants produces pe- 

 culiar to itself. How remarkably these secretions of dilfcrent plants vary 

 from each other, frequently in the same plant! The peach tree affords a fa- 

 miliar example of this; the gum of this tree is mild and mucilaginous; the 

 bark, leaves and flowers abound with a bitter secretion than which nothing 

 can be more distinct from the gum ; the fruit is replete not only with acid, 

 mucilage and sugar, but with its own peculiar aromatic and highly volatile 

 secretion, on which its delicious flavor depends; the pit also contains pru.ssic 

 acid to a certain extent. Can any one among the scientists tell us how the 



