

\ 1ICAL CLASS-BOOK OF HOT 



flow of the sap ia always most rapid when tin- vital action 

 is strongest. In the spring, when the buds of the pre- 

 vious year are expanding into leaves ; and in summer 

 when the bails fur the coming year are just beginning 

 to be fiirnieil, tliere is a strong determination of sap to 

 the cxtrcmilii >. Light. Heat, Electricity and Winds. 

 accelerate the vital forces, and produce some remark- 

 able effects, which they could only do by virtue of th 

 existing vitality ; and it is highly probable that the 

 circulation of the fluids is more or less strongly impelled 

 by all these forces. Light exerts a powerful influence on 

 the leaves directly, and through them, indirectly, on the 

 whole system. Vegetation is always more rapid and 

 powerful in warm than in cold climates; and it is said 

 that no natural degree of heat would prove injurious, 

 provided there is also a sufficiency of moisture. Winds 

 not only afford mechanical exercise ; but they lave the 

 whole system in fresh currents, which are thus driven 

 through the pores of the leaf, and carry electrical stimu- 

 lants into the whole circulation. When a plant dies the 

 flow of the sap is restrained, and the Endosmose is at once 

 .irn^tcd. Thus you sec that no merely mechanical 

 agency can satisfactorily account for the actions of living 

 beings. They have machinery, it is true, and this must 

 be moved by mechanical agency; but the MOVJM. i -o\vi:i: 

 i-tainls back of all ; for the structure, in being vitalize'!, 

 passes away from under the common laws of dead matter. 

 170. CHOICE OF NUTRIMENT. That plants do have 

 a power of selection, or a kind of choice in the substances 

 that surround them, is' absolutely certain. From the 

 self-same soil a Beet-root, or Potato, will take up potash, 

 a Clover-plant lime, and Wheat, jihosphorio acid for the 

 elaboration of its seed, and silex for the support of its 

 stalk. It has also been observed that roots lengthen 

 most rapidly in the direction of the most favorable con- 

 ditions, thus appearing to seek, by a kind of instinct, the 

 water and gases that arc to be found in richer soils. 

 But the idea of their being governed by instinctive pre- 

 ferences is now wholly exploded. We can easily see 

 that they must grow most rapidly where they find the 

 best means of growth ; and thus literal and prosaic 

 Science very coolly sets Poetry aside. 



CM AI'TKi: XIV. 



TIIK r.\'i>. 

 171. A tree should not be considered as a single 



tto plant* chooM tbelr (bod? It It an Instinctive proem? II 



ub)rt Wht may a Tw be cnnridered T Define Bn.l W I..T.. 



i but rather as a compound being, consisting 

 of as many individuals as it may contain buds. 



172. A Hud is a scaly t nrrlnjir , / the 

 rudiments of a new plant, tijiich il halih in n i 

 state, >>>il it circumstances farur l/nir <! 



At figs. 10 and 11 arc different forms of the BCD. The. 

 trees and shrubs of warm climates do not form scaly 

 buds, but unfold their leaves directly to the air. When- 

 ever there is snow a part of the year, and severe frosts 

 occur, buds arc produced for the protection of the latent 

 plantl 



173. STRUCTURE OF THE BUD. In this is found one 

 of the most beautiful provisions of life. The young 

 Plant is enveloped in a coat of downy fibre, with la\er 

 upon layer, to make it soft and warm. Its roof is 

 thatched with stronger folds ; and over the whole is 

 spread a coat of resin, which renders it impenetrable 

 both to cold and wet. Thus wrapped in its silken 

 swaddling clothes, the Plantlet sleeps securely in its 

 warm retreat, until the latent power is excited, and it 

 comes forth to join the troop of dancing leaves, and re- 

 joice in the greenness of Spring or perhaps to assert its- 

 individuality by the assumption of a new life. 



174. The Embryo Plant remains latent in the bud, 

 as it often does in the seed, and will not grow till it is 

 placed in circumstances favorable to its development. 

 But that it Joes exist in the bud, and has the capacity "f 

 unfolding itself into a new plant, is shown 1>\ the familiar 

 operations of Grafting, Layering, and Budding, which 

 consist simply of transferring the bud to conditions where 

 its specific vitality may be excited, and its individual life 

 called forth. 



175. The Plumule, or ascending portion of the stem. 

 originally consists of a growing point, or, in other words, 

 a lux!, which, in its undeveloped state, exists in the 

 embryo. 15y the development of this a section of stem 

 is produced, still terminated by a bud, which always 

 lini-hes and crowns (lie annual growth. In some trees, 

 as the White Birch and Cherry, the primary ax: 

 principal stem, continues to maintain its ascendency ; and 

 wi!h its aspiring point annually crowned by a new leaf- 

 bud, it remains distinct from the branches. But in must 

 cases, by repeated ramifications, it becomes indistinguish- 

 ably merged in its own offshoots; and at the summit 

 several points of about equal height appear, neither of 

 which has any special claim to the distinction of belong- 

 ing to the primitive stem, as we often sec in tlie Lime 

 ind Api'lc-t 



aro scaly bud* formed ? Where not formed ? Structure of tho l!ud, describe. 

 Embryo, proof* of lit eilttance In the bud. I'rocosa of It* development ami 

 vegetation, deacrlb*. Primary axla, In what trees dtotlnuulshable J In what notf 



