238 



MONTHLY JOURNAL OF AGRICULTURE. 



plex combinations and energetic qualities ; I 

 all, indeed, that is hurtful as poison, useful as 

 medicine, valuable in the arts, applicable as 

 food, or otherwise capable of being rendered 

 subservient to human economy, is more or 



less dependent upon this elaboration of the 

 sap. There are differences of opinion, as 

 previously stated, as to the mode of vital ac- 

 tion and the ultimate organization by which 

 these results are eftected. Even the theory 

 of vegetable respiration, once considered to 

 be established beyond the possibility of doubt, 

 and supported by numberless experiments 

 apparently the most conclusive, is no longer 

 a settled point in physiology. Some very 

 nice distinctions have been made between 

 the process in question and that of digestion, 

 to which the leaves are likewise subservient; 

 but neither of these operations are sufficiently 

 obvious in the experiments hitherto per- 

 formed on growing plants to enable us to sep- 

 arate them. By whatever name we desig- 

 uate the source of these modifications of the 

 vegetable juices, and whether we regard it 

 as a simple or a binary pi'ocess, it is accom- 

 panied by a large amount of exhalation. A 

 common sunflower, three feet high, is found 

 to exhale one pound and a quarter of fluid, 

 chiefly water, every day ; and the conunon 

 cabbage nearly as much. This exhalation is 

 ascertained to be chiefly through the medium 

 of the leaves ; and, consideiing their corre- 

 sponding functions, is analogous to the watery 

 exhalation that accompanies the action of the 

 lungs in animals. That the stomata are con- 

 cerned in the disposal of this superfluous 

 moisture seems to be very evident, as in suc- 

 culent jilants, and others growing in situa- 

 tions subject to long-continued drouth, these 

 openings are generally very sparingly dis- 

 ti-ibuted, while they are most numerous in 

 tluiKt; ihat derive large STipplles f)f water 

 from the soil in which they niiturally veget- 

 ate. Led away by this facl, and contem- 

 plating the vast quantity of water exhaled 

 (478) 



by plants possessing numerous stomata, some 

 physiologists of the present day seem inclined 

 to deny the instrumentality of the latter in the 

 admission of air to the interior substance of 

 the leaf ; regarding them only as organs of ex- 

 cretion, like the pores of the ani- 

 mal skin. 



The reciprocal action of the spi- 

 ral vessels is no less a subject of 

 dispute thati that of the stomata, 

 and on a similar one-sided view of 

 their structure and situation ; al- 

 though no authenticated instances 

 can be adduced of their containing, 

 at any period after their first de- 

 velopment iu the tissue of the plant, 

 anything but air ; and they are tor 

 the most part only traceable in 

 those portions upon which these 

 curiously adapted openings exist — 

 so uncertain is our actual knowl- 

 edge of the jjheuomena of vegeta- 

 ble growth, and of the vital func- 

 tions which they indicate ! In fact, 

 there is scarcely any branch of 

 physical science so little understood 

 as that of Vegetable Physiology. 



By examining the interior of the 

 human body after death, and com- 

 paring the relative situations of its various 

 organs with the functions and sensations of 

 the living, we are enabled to decide with a 

 tolerable degree of certainty upon their real 

 agency in the system ; and, on dissecting 

 other animals and finding organs in similar 

 situations and bearing similar relations to 

 each other with those of the human body, 

 we are justified in drawing our inferences 

 accordingly. And in this manner, descend- 

 ing from one to another through the va- 

 rious grades of the animal kingdom, wo 

 have arrived at a comparatively correct es- 

 timation of tite grosser elements of their 

 existence ; but the organization of veget- 

 ables is so perfectly distinct from our own 

 and that of all the higher classes of an- 

 imals, that it is impossible to draw any cor- 

 rect conclusions by mere comparison. We 

 can, indeed, trace the gradual gi'owth and 

 development of their parts, and observe the 

 loss of vigor and the debility which precedes 

 decay, and from other concomitant circum- 

 stances consider them as exceptions to the in- 

 ertia of matter ; in other words, as being en- 

 dowed with that hitherto incomprehensible 

 principle, life. We can proceed a few steps 

 farther by dissection, and, discovering a sys- 

 tem of vessels ti'a versing the plant through- 

 out its whole substance, are led to conclude 

 that life here, as in animals, is dependent 

 upon a continually repeated elaboration and 

 modification of the fluids they contain ; nay, 

 the microscope shows us those fluids in mo- 

 tion, and almost in the act of depositing the 

 j)etty molecules that contribute to the growth 

 of the tissue. There we stop. Gomparisou fails 

 tu asnisl our iebearches any iarlher ; and ex- 

 periment, often Ibunded on the uncertain basis 

 of bare conjecture, is our only guide beyond. 



