BOTANY. 



Vegetable only sterile spot of a garden, sent forth innumerable 

 Physiology. s t a lk s an d roots to the more fertile surrounding 

 ~'~" ground. 



It is a fact familiar to everyone that has traversed 

 hilly wooded districts, that trees, particularly pines, 

 which grow on bare rocks, will send out their roots 

 in every direction so as to reach the soil below. It 

 is difficult to explain the manner in which this is ef- 

 fected : it certainly cannot be referred to any vo- 

 luntary power ; a mere change of position might be 

 referred to such a power, but it is impossible to con- 

 ceive any increase of parts from any effort of will, 

 supposing its existence to be unquestioned, which is 

 not the case. Mr Knight resolves it on mechanical 

 principles. Objections, however, will probably be 

 as strong against this hypothesis as against the other 

 supposition. The truth is, that the fact is all that 

 we can know, until we can render the vital prin- 

 ciple palpable to our senses, which none but a mad- 

 man can conceive possible. 



Excretion The root is also supposed to exhale or excrete mat- 

 from root. ( erj as jt is not uncommon to find the earth surround- 

 ing it impregnated with a gelatinous matter. 



We have now seen that the radicle, or true root of 

 physiologists, consists chiefly of cellular substance, 

 and of a continuation of the sap vessels, through 

 which the food of the plant is conveyed into its cir- 

 culatory system ; we have also seen that the whole 

 of the root, commonly so called, is composed of 

 various solid parts, similar to those of the stem, which 

 are pervaded by numerous cells and continuous ves- 

 sels, and are probably furnished with a secretory ap- 

 paratus. Each of these several organs we have found 

 to perform important functions ; and although we 

 can only catch an imperfect glimpse of them, we have 

 seen enough to convince us, that inscrutable wisdom 

 alone could have given existence to such beautiful 

 contrivance. 



We are not aware of the particular chemical 

 changes which are produced in the root : the gene- 

 ral changes induced by vegetation (in which the root 

 may be considerably concerned) shall be discussed 

 after we have completed our more particular views of 

 the vegetable system. 



SECT. III. Of the Stem. 



Stem- We now come to the stem, or caudex ascmdens, 



(Part I. Sect. ii. Art. 6.) one of the most valuable 

 parts of the vegetable kingdom, in whatever point of 

 view we regard it. Between the stem and the root 

 lies the intermediate stem (caudex intennedius), and 

 which is composed of the same parts and vessels with 

 the stem itself. 



Structure Consistently with our general plan, we shall now 

 ot'ligueous examine the structure of ligneous stems, which are 

 stems. t jj e most p tr f ect- Among these are the trunks of 

 trees ; which consist of the cuticle, the bark, the 

 liber, the alburnum, the wood, the pith, and the va- 

 rious vessels which have been fully described in the 

 preceding Section. The chief difference between 

 these parts in the root and in the stem seems to be, 

 that in the latter they are more distinctly character- 

 ised, and consequently less easily confounded with each 

 other. The vascular system is also a mere coutinua- 

 6 



tion of fchat of the root, and casnot be described in any VegetaUl 

 other way tha as a small part of an extensive series. Physiolog 

 Mrslbbetson has bestowed much attention on this sub- ' " J~* 

 ject, and divides the trunk of a tree into 1. Rind; 2. 

 Bark, and inner bark ; 3. Wood ; 4. Spiral nerves ; 5. 

 Nerves, or circle of life ; 6. Pith. A variation in 

 the nomenclature in such an outline as we could give, 

 would be the chief apparent difference between this 

 arrangement and that which we have sketched. She 

 indeed details minutely a variety of topics, into which, 

 however, we cannot enter, for the same reasons that 

 influenced our plan in the description of seeds. We 

 may here remark, that it is a matter of no trifling 

 import to attend to some general nomenclature in 

 vegetable physics. The diversity of names now in use 

 for the same organs, has, without doubt, given rise 

 to much of the vagueness of all researches in this 

 branch of science. Correctness and precision are 

 peculiarly required in all physiological inquiries. 

 L'gntrous stems have been subdivided into several 

 species, of which it is right to take some notice, as 

 the subdivisions are natural, and are commonly adopt- 

 ed even in familiar conversation. They are as fol- Division, 

 lows: 1. Trees; 2. Shrubs; 3. Pine tribe; 4. Palms. 

 The first, second, and third, contain all the parts de- 

 scribed as forming a perfect ligneous stem, and are 

 distinguished by their respective modes of branching 

 and of bearing leaves. The last is composed of those 

 plants which are usually called monocotyledonous,to 

 which the palms belong, whose structure is so very 

 remarkable, that we shall enter pretty minutely into 

 the detail of their peculiarities ; but, in the first 

 place, it will be necessary to determine the charac- 

 ters of all the other species of ligneous stems. Trees Trees, 

 and shrubs are distinguished from each other by the shrubs, 

 disposition of their branches, and are, as might be 

 expected, mutually convertible by change of soil, 

 of climate, or any other variation in the culture. In 

 both buds are formed at the bases of the foot-stalks, 

 which shoot out and become branches ;. but in the 

 former these branches are chiefly confined to the 

 higher parts, and in the latter, to the lower parts of 

 the stem. It is impossible to point out the bound- 

 ary that separates the two, as they pass so insensibly 

 into each other. The stems of trees and shrubs origi- 

 nate in the plumule (Fl.LXXI. Fig. 1.), as every as- pi. LX> 

 cending stem does ; every year new organs are formed, Fig. 1. 

 and the increase goes on so long as the vitality of the 

 plant is in full vigour. No certain limit has been hi- Size, 

 therto discovered to the growth of ligneous stems, for 

 we see them increasing in magnitude far beyond the 

 recollection of man, and we know not when it is to 

 cease. Two facts connected with this subject has been 

 determined, and it is this, that there is great variety 

 in the dimensions of different species, and that some 

 possess the power of increase very differently from 

 others. One class of trees vegetate with extraordina- 

 ry rapidity ; of thip we have remarkable examples in 

 the poplar and willow : others again are as noted for 

 the slowness of their growth, as the oak. Many 

 instances of the enormous magnitude of trees are re- 

 corded. Pliny mentions a tree (Platanus) in the 

 hollow trunk of which, Lucian the Roman consul 

 supped and slept with twenty people. Humboldt 

 saw a large tree, the diameter of which was 17 feeU. 



