t62 THE PLANT WORLD. 



85 drops of liquid falling in one minute from a tip of a leaf of Colo- 

 cassia esculenta. From the young leaves of certain aroids, water is 

 sometimes thrown in a fine jet to the distance of a few inches. In 

 these cases, the liquid escapes through rifts. Nectar-glands do not 

 facilitate the escape of water; they are formations to attract insects. 



It is easy to understand why the sap flows freely in early spring. 

 In cold weather, the woody tissues of a plant are filled with starch or 

 other solid matter laid up during the previous season. Mild weather 

 induces chemical changes. More water is absorbed, the solid parts 

 are liquidized; they expand, trying to occupy greater space, press 

 against the cell walls, burst them and find an outlet through any in- 

 cision or crack. The farmer knows this, and prunes his vines in 

 February, or before they begin to bleed too freely. The boisterous 

 month of March is the one of all others in which this change goes on 

 The trees and vines are already awakened from their winter's nap; 

 buds are swelling, some trees are flowering, the sap is running. The 

 yearly miracle of the resurrection of the plant world is about to take 

 place. 



Cell-sap is the fluid contained in the vacuoles, or spaces in cells 

 unoccupied by protoplasm, principally water in which are dissolved 

 salts gathered from outside sources, and starchy or sugary substances 

 manufactured by the plants themselves. When cells do not touch 

 each other on every side, intercellular spaces are created. These may 

 occur in spots {lacunce), or long-drawn out canals, and are also re- 

 ceptacles for various secretions, assisting to conduct the sap. Such 

 intercellular spaces are the resin passages of pine trees, forming con- 

 tinuous systems throughout the trees. The contents of cells, speak- 

 ing generally, are, besides chlorophyll, starch, lichenin (such as the 

 starch of Iceland moss), dextrin, a soluble, gummy substance, made 

 from starch by the action of heat, and minute drops of oil, usually 

 associated with albuminoids. The sap wood of deciduous trees is 

 pale in color, and is found in the newest or outermost rings. It is 

 called alburnum. In these the woody cells are thickened but per- 

 vious. The dry heart wood is the duramen, in which the thickened 

 cells are solid and impervious. By means of stomata in leaves of 

 dicotyledons, the surplus water finds a natural outlet ; (through chinks 

 or rifts in monocotyledons). 



In many plants the juice is thick and milky, called latex. As 

 children, we were familiar with the milky juice of dandelions and 

 milk-weeds and the brown stains it left on our hands. Plants of this 

 sort are the Papaveracese, Asclepiadaceas, Campanulaceae, Convol- 

 vulacese, Apocynacese and Euphorbiaceae. The walls of latex cells 

 are soft, thin, easily compressed, so that if the stem be cut, the 



