i 



86 



WHY PLANTS (JKOW, 



also absorbed l)y tlio leaves, citlicr from diops of lain or dew, or from the vapour of 

 wiitor in the air. Air is lar</t'ly absorbed by the K-uves, and some also by the roots, 

 c?ither as diSsolveil in water, or else ilirectly from the crevices and pores of the 

 soil, which are lilled with air. 



264. J '/(Hits ahtiin'h til' ir I'iioil hi/ (luir siir/'xi'r. Animals have an internal cavity, 

 — a tifoniar/i, — to hold (heir food; and from the stomacli it is taken into the 

 svstem. Plants have nothin<' of this kiml. Tlify ab.soil> tlieir food by their stir- 

 face, — by the skin, as it were; and when very yonn<,' and with the whole sur- 

 face fresh and thin, l»y one pait almost as much as another, Ihit as they ^rovv 

 older and the skin hardens, i hey absorb mostly by their fresh rootlets and the tips of 

 the roots, and by the leaves, — the former spread out in tiie soil, the latter spread 

 out in the air. For whih^ the skin oi- l)ark of the older parts of the roots is harden- 

 ing, new tips and rootlets are always forming' in ^rovvin«^' plants, with a fresh sur- 

 face, which absorbs freelv. And as to the leaves, tliey an; renewed cverv vear 

 (even everjL^reens produce a new crop annually, and the old ones fall after a year 

 or two); and the skin of every leaf, especially that of the under side, is riddled 

 with thousands of holes or little mouths (called liri'dthhtii-jxn'Oi), which open into 

 the chambers or wiudiii<,' ))assa^'cs of the pidp of (he leaf, so that the air may 

 circulate freely throUjLrhout the whole. 



265. Plants ahxiirh iln'ir fuml all i)i i]ii> Jlulil fitnii. They are unable to take 

 in anytliitif; in a solid state. They iinhihr or drink in all their food, iti the form of 

 water, with whatever the water has dissolved, and of air or vapour, by one or both 

 of which tlieir leaves and roots are surrounded. The reason they imliibe only fluid 

 is this. The roots, leaves, and all the rest of the plant, inider the miero.scope, are 

 seen to be made up of millions of separate little cavities, each cut off from the 

 surrounding ones by clo.sed })artitions of membrane. All t hat the platits take into 

 their system has to pass through these partitions of membrane, — which fluid (air 

 or moi.sture) alone can do. 



266. The connnon juices of [)iants are called Sap. What they take in from the 

 soil and the air, not being digested or made into vegetable matter, is called Crude 

 Sap, All that the roots imbibe has to be carried up to the leaves to be digested 

 there. So while the roots are ab.sorbing, the stem is 



267. Conveying the Crude Sap to the Leaves, 'i^hei-e is no separate set of vessels, 



and no open tubes or pipes for the sap to rise through in an unbroken stream, in 

 the way people generally suppose. The stem is made up, like the root, of cavities, 



I 



