*lfi 



SCIENCE OF AGRICULTURE. Part II. 



If ii be asked of what are the elemental} organs themselves composed, the reply is. they 

 are composed, as it appears from the same analysis, of a fine, colourless, and transparent 

 membrane, in which the eye, aided l>y the assistance even of the best glasses, can discover 

 no traco> whatever of organisation ; which membrane we must also regard as constituting 

 the ultimate and fundamental fabric of the elementary organs themselves, and, by conse- 

 quence, of the whole of the vegetable body. It lias been asked by some phytologista 

 whether <>r not plants are furnished with vessels analogous to the blood-vessels of the 



animal system. But if it be admitted thai plants contain fluids in motion, which cannot 

 possibly be denied, it will follow, as an unavoidable consequence, (hat they are furnished 

 with \essels conducting or containing such fluids. If the stem of'a plant of marigold is 

 divided by means of a transverse section, the divided extremities of the longitudinal fibres, 



arranged in a circular row immediately within the hark, will he distinctly perceived, and 

 their tubular structure demonstrated bymeansofthe orifices which they present, particu- 

 larly when the stem has begun to wither. Regarding it, therefore, as certain, that plants 

 are furnished with longitudinal tubes, as well as with cells or utricles for the purpose of 

 conveying or containing their alimentary juices, we proceed to the specific illustration of 

 both, together w ith their peculiarities and appendages. . . 



I 179 The utricle* are the One ami membranous vessels constituting the cellular tissue of the pith and 

 pulp already described, whether Of the plant, flower, or fruit Individually they resemble oblong bladders 

 inflated in the middie, as in the case of some plants ; or circular or hexagonal cells, as in the case ol 

 othera Collectively they have been compared to an assemblage of threads ol contiguous bladders, or 

 - ,.r to the bubbles that are found on the surface of liquor in a state of fermentation. 

 'The tube* are the vessels formed by the cavities of the longitudinal fibres, whether as occurring in 

 the stem of herbaceous plants, or in the foot-stalk of the leaf and flower, or in the composition of 

 the cortical and ligneous layers, or by longitudinal openings pervading the pulp itself, as in the case of 

 the vine. 



ISM. n. Earn tub?, are tul.es distinguishable by by betas; twisted from right to left, or from left to 



Uieraperiorwidthofthediameterwhich they present 187 right, >>• die form of a corkscrew. Ihev occur in 



on the horizontal section of the several part, of die ^mtfyrr*. """' » , «maance tn herbaceous plants, particularly 



il hi e$crC£c£rSffl in aquaucs. 



13S^>. Simple tuba { Ps- 1ST.) are the largest of all jftTirmiT ,3 * 5 " ' '"'"' ''"'"' '"*" "etobesappaiBntlj spiral 



large tubes, ami are formed of a thin and entire mem- on a slight inspection, but which, upon minute 



brine, without anv perceptible disruption of con- examination, are found to derive their appearance 



tinuilv. The, are found chiefly in the bark, though merely from their being cut transversely by parallel 



not confined to it. as they are to be met with also in Mi Hssures. ..... 



the alburnum and matured wood, as well as in the 1386. .Virol Rita are rubes combining in one m- 



libres of herbaceous plants. i ; j dividual two or more of the foregoing varieties. 



._—.__ ' .... . . . < . .» . ■ ■ I i . i ll^l. ,1 ..11 > , ..- lliA.n ,■> » 1 ,»i .- -i ... . ,f t li . ■ Ulitiill'lis. 



lum ui iitiiMtuiin i 'mitt.-. -■- - -- " . , rin 



P tuba re-en.ble the simple tubes in their Elifl .Mirbcl exemplifies them in the case of the Hiitoiiius 



general aspect ; but differ from them in being pierced I II 111 umbellate, In which the porous tubes, spiral tubes, 



with small holes or pores, which are often distributed and false spiral tubes, are often to be met with united 



in regular and parallel rows. They are found in in one. 



most abundance in woody plants, and particularly in f ' l 38 '- "' "»"" luha ?, re tubes composed of a s ic- 



wood that is linn and compact, like that of the oak ; , I 1 cession of elongated cells united, like those of the 



but thev do not, like the simple tubes, seem destined I ' cellular tissue. Individually they may be compared 



to contain anv oily or resinous juice. EU ' Mil to the stem of the grasses, which is fornied of sevcal 



1384. Si .• tine, transparent, and thread- ^i-Jjllil> r internodia, separated bv transverse diaphragms; and 



like substances ... , a,i illy interspersed with the -*-HM^ collectively to a united assemblage of parallel and 



other tubes of die plant, but distinguished from them collateral reeds. 



1388. Pores are small and minute openings of various shapes and dimensions, that seem to be destined 

 to the absorption, transmission, or exaltation of fluids. They are distinguishable into perceptible pores 

 and imperceptible pores. . 



1389. Gaps, according to Mirbel, are emptv, but often regular and symmetrical, spaces formed in the 

 interior of the plant by means of a partial disruption of the membrane constituting the tubes or utricles. 

 In the leave- of herbaceous plants the gaps are often interrupted by transverse diaphragms formed Of a 

 portion of the cellular tissue which still remains entire, as may be seen in the transparent structure ot the 

 leaves of 7ypha and many other plants. Transverse gaps are said to be observable also in the bark ot some 

 plants, though verv rarely. 



There are varum* appendages connected with the elementary organs, such as internal glands, 

 internal pubescence, oic. : the latter occurs in dissecting the leaf or flower-stalk of Nuphar lutea. 



Chap. III. 



Vegetable Chemistry, or Primary Principles of Plants. 



1391. As plants are not merely organised beings, !>ut beings endowed with a species of 

 life, absorbing nourishment from the soil in which they grow, and assimilating it to their 

 own substance by means of the Functions and operations of their different organs, it is 

 plain that no progress can be made in the explication of the phenomena of vegetable life, 

 and no distinct conception formed of the rationale of vegetation, without some specific 

 knowledge of the primary principles of vegetables, and of their mutual action upon one 

 another. The latter requisite presupposes a competent acquaintance with the elements 

 of chemistry ; and the former points out die necessity of a strict and scrupulous analysis 

 of the several compound ingredients constituting the fabric of the plant, or contained 

 within it. If the object of the experimenter is merely that of extracting such compound 

 ingredients as may be known to exist in the plant, the necessary apparatus is simple, 

 and the process ease : but if it be that of ascertaining the primary and radical principles 

 of which the compound ingredients are themselves composed, the apparatus is then 

 complicated, and the process extremely difficult, requiring much time and labour, and 



