.> 



r 

 ■ J 



^^ 



ELEMENTARY BOTANY. 



218. Leaves are functionally the most active of the organs of vegetation. In 

 wemis chiefly conducted digestion ov Assimilation^ a name given to the process 

 vluch accomphshes the following results :— 1. The chemical decomposition of the 

 <^ygenated matter of. the sap, the absorption of carbonic acid, and the liberation 

 V\l ^^^'^^^ ?* *^^ ordinary temperature of the air.. 2. A counter-operation by 

 Wiucti oxygen is absorbed from the atmosphere and carbonic acid is exhaled. 



h K ''^^^^?^^^^*^^^ ^f the residue of the crude sap inta the organized substances 

 wtiich enter into the composition of the plant. The exhalation of oxygen appears 

 w take place under the influence of solar heat and light, chiefly from the under 



" an K s^ ^^^^' ^^^ t^ ^^ ill some measure regulated by the stomates ; the ab- 

 sorption of oxygen goes on always in the dark, and in the daytime also in certain 

 cases., . Ihe transformation of the sap is effected within the tissnes of the leaf, and 

 2IQ^^t1 l^^^^^^^y ^^^^ ^^ l^ss throughout the active parts of the whole plant. 

 ' th Floral Organs seldom contribute to the growth of the plant on which 



ey are produced ; their functions are wholly concentrated on the formation of 



stain ,-^^.^^^.^*^'^ (calyx and corolla) acts in the first instance in protecting the 



the ^^ f " 1 P^^*!'^>^^^^*i^^g tlie early stages of their development. When expanded, 

 odou^^fll brilliant colours which they often display, of the sweet or strong 



infln ^ ' ^'^^^> h.^s not been adequately explained. Perhaps they may have great 

 to bp ^^*^ '^ attracting those insects whose concurrence has been shown in many cases 



221^^'Tnf^^^ fp^ the due transmission of the pollen from the anther to the stigma, 

 the v' Pistil* when stimulated by the action of the pollen, forms and nourishes 



Qonx^^^^^^f" T^® varied and complicated contrivances by which the pollen is 

 the a + ^ stigma, whether by elastic action of the organs themselves, or with 

 of jj^^^^^^?^^^ of wind, of insects, or other extraneous agents, have been the subject 

 and r^^'^'^^ observations aud experiments of the most distinguished naturalists, 

 tnown^ ^^^1 \^^ ^^^^ Ijcing fully investigated. Their details, however, as far as 



22^ n f V® f^^ *oo long for the present Qutline. 

 promot + A^^^ nourishes and protects the seed until its maturity, and then often 

 circumsl^ tUsj^ersion by a great variety of contrivances or apparently collateral 

 by the d *^^^^' ^*^'' ^^' ^^ elastic dehiscence which casts the seed off to a distance ; 

 tiem to^Ko ^^^^?^* ^^ ^ pappus, wings, hooked or other ai)pendages, which allows 



^em to kT • ^ p<ippus, wings, hooked or other ai)penaages, wnicn allows 



V their ,*;^™^*? ofl' by winds, or by animals, etc., to which they may adhere ; 



-Ai. r ^^^11 specific gravity which pTinKlf^a t.hAin fn flmif. down streams ; bv their 



^ous to birds, etc., who taking 

 ^tc- Appendages to the seeifg 



ipecific ^ 



taoc*^^^?^ ^^ '^^^^^' ^^^'> '^^o taking them for food drop them often at great dis- 



223 XI ' ""i^F^^uHges to tne seei ^ 



leaves irf^^i ^^^ various functions. The ordinary indumentum (171) of stems and 

 some oc • ^^^Kis to take little part in the economy of the plant besides perhaps 

 h^g /2l^fif ^°^^ protection against injurious atmospheric influences, but the root- 

 anpear i^ ^^^ active absorbents, the hairs on styles and other parts of flowers 

 Panduk if Baaterially to assist the transmission of pollen, and the exudations of 

 P*ienom t^ ^^'^' ^^ ^^^ ^^*^" ^^^ copious not to exercise some influence on the 

 ^Winfl^^ vegetation. The whole question, however, of vegetable exudations and 

 r ^^ence on the economy of ve<^etable life, is as yet but imperfectly understood. 



^^p. IV. Collection, Pk£S£rvation, and Determination of Plaints. 



i^reahlv }^^^ ^^^ undoubtedly be most easily and satisfactorily examined when 

 %irabl f ^^^^* '^^^^ *™^ will rarely admit of this being done, and it is moreover 

 '^ns mn2^ f^^^^^"^^ ^^^^^ wi^^ *^^^^^ plants previously observed or collected. Specif 

 ^or fiX-t *p^^f^^e» ^e selected for leisurely observation at home, and preserved 

 rv.. ^^e reference. A collection of such sj>ecimens constitutes a Herbanutn. 



C>oth o,^ , ^*^^ Specimen, to be perfect, should have root, stein, leaves jtowcrs 

 *Iwavs\!r ^?, '" ^"^^) and fruit (both younc; and mature). It is not, however, 

 •^inpleten - *° S'lther such complete specimens, but the collector should Him at 



- wv. ^auu^ji sucu complete S[)eClUJeu», uuu mu,^ yy^^^^^ - - 



WS''*lT'^^r\. F'*agments, such as leaves without flowers, or Bowers without 

 ^> are of Uttle orno use, .^.4 --^"V- : 



■ ■- >^ ■ > " ^ ■ ^ ■ .. r ■ i ■ - ... .■ -* . . -f.'.- =-r >,• 4- ^ ^ -^ . -r^. . >. 



.- \''-- 



- '- - - 



