216 SCIENCE OF AGRICULTURE. Part II. 



whether or not plants are furnished with vessels analogous to the blood-vessels of the 

 animal system. But if it is admitted that plants contain fluids in motion, which cannot 

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

 with vessels 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 bark, will be distinctly perceived, and 

 their tubular structure demonstrated by means of the 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 with their peculiarities and appendages. 



1353. The utricles are the fine and 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 middle, as in the case of some plants; or circular or hexagonal cells, as in the case of 

 others. Collectively they have been compared to an assemblage of threads of contiguous bladders, or 

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



1354. The tubes 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 compositron of 

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

 the vine. 



1355. rAZar^e<6e are tubes distinguishable by the 229 twisted from right to left, or from left to right, in 

 superior width of the diameter which they present on ^.--.u_ *^^ form of a cork screw. They occur in most 

 the horizontal section of the several parts of the ^SSkS^ abundance in herbaceous plants, particularly in 



1356. Sjij>/e<6ei(.fe.229.) are the largest of all the ||WJ|I||II||I|| jl 1559. False sptraZ <!*/) are tubes apparently spiral 

 large tubes, and are formed of a thin and entire mem- nliniiltlllll " ^ slight inspection, but which, upon minute 

 brane, without any perceptible disruption of con- Kl| ||| l|ji||| examination, are found to derive their appearance 

 tinuity, and are found chiefly in the bark, though not HI h|| ||||ffl merely from their being cut transversely by parallel 

 confined to it, as they are to be met with also in the VI | h|I |ll|| fissures. 



alburnum and matured wood, as well as in the fibres n|| |l| fi|i|| 1360. Mixed tubes are tubes combining in one In- 



of herbaceous plants. mm |tl ill | dividual two or more of the foregoing varieties. 



1357. PoroiM <6e resemble the simple tubes in their H l|| ||| | Mirbel exempUfies them in the case of the butomus 



general aspect; but differ from them in being pierced |1| |Uv|l|| | umbellatus, In which the porous tubes, spiral tubes, 



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



in regular and parallel rows. They are fuund in Mllliyllllll in one. 



most abundance in woody plants, and particularly in llffilinilllll R 1361. TAe^maW teftcsaretuhescomposedofasucces- 



wood that is firm and compact, like that of the oak : fflilii||ll|iH sion of elongated cells united, like those of the 



to contain any oily or resinous juice. ^Ulllilll lir to the stem of the 

 - Itubes " ..... - -i....!!..' .. . 



but they do not, like the simple tubes, seem destined lillliiliillllllll|jj cellular tissue. Individually they may be compared 



" " grasses, which is formed of several 

 I,, separated.lby tr^ 

 like substances, occasionally interspersed with the other collectively to a united assemblage of parallel and collateral 



1358. Spiral tubes are fine, transparent,'and thread- ^mmiLP^ internodia,; separated.lby transverse diaphragms ; and 



ke substances, occasionally interspersed with the other colled ' " 



tubes of the , plant, but distinguished from them by being reeds. 



1362. 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. 



1363. Gaps, according to Mirbel, are empty, but often regular and symmetrical spaces formed in the in- 

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

 In the leaves 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 of the 

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

 plants, though very rarely. 



1364. Tliere are various appendages connected with the elementary organs, such as internal glands, 

 internal pubescence, &c. : the latter occurs in dissecting the leaf or flower-stalk of nymphaea lutea. 



Chap. III. 

 Vegetable Chemistry y or Friinary Principles of Plants. 

 1365. As plants are not merely organized beings, but 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 the necessity of a strict and scrupu- 

 lous 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 appara- 

 tus is simple, and the process easy. But if it is 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 labor, and much previous practice in analytical research. But whatever may be the 

 object of analysis, or particular view of the experimenter, the processes which he employs 

 are either mechanical or chemical. 



J^m. The mechanical processes are such as are affected by the agency of mechanical powers, and are 

 often mdeed the operation of natural causes ; hence the origin of gums and other spontaneous exudations. 

 But the substances thus obtained do not always flow sufficiently fast to satisfy the wants or necessities of 

 man. And men have consequently contrived to accelerate the operations of nature by means of artificial 

 aid in the application oi the wimble or axe, widening the passages which the extravasated fluid has 

 lorced, or opening up new ones. But it more frequently hapi)cns that the process employed is whoUy 



