1839] 



FARMERS' REGISTER. 



203 



altogether in the screen shoot of each year, wliilst 

 the older portions of the stem undergo no change 

 in dimensions, is proved by the Ibllovving liict, 

 known, I presume, to all. VVhen a name is cut 

 upon the bark of the beech tree (^fagus sylvatica,') 

 the tree may continue to grow until it has doubled 

 its original height, but the name will never be 

 raised Tlirther from the ground than the point at 

 which it was originally cut. This process is tlie 

 fsame both in exogens and endogens. It general- 

 ly happens, that some oC the buds with which a 

 stem is i'nrnished at the axil of every leaf, grow, 

 and originate branches. Wiien this is the case, 

 the growth of these branches is precisely similar 

 to that of the stem from which they sprung. The 

 only thing which seems at variance with this ac- 

 count of the growth of a stem, is the absence of 

 all branches from the lower part of it, that part 

 commonly called tlie trunk. From this, some have 

 inferred, that the portion of the stem which was 

 originally included between the root and the low- 

 est branch formed, which is generally not more 

 than a foot or IS.inches in lenirlh, has subsequent- 

 ly expanded into the trunk. The true reason why 

 there are no branches on the trunk, is, not that 

 branches were never formed there, but that alter 

 they were formed, they have died and disappear- 

 ed, from the operation of causes, which have been 

 already explained, when treating of the tendency 

 manifested by stems to a perltjct reguiariry ol' 

 growth. 



The increase of a stem in diameter is owing, first 

 to the developement of the cellular tissue, which 

 grows in every direction ; and second, to the pro- 

 duction of the vascular and woody tissues. The 

 horizontal expansion of the cellular system, is si- 

 multaneous with its growth in an upward direction, 

 so that a young stem increases in diameter to a 

 certain extent, at the same time that it grows in 

 height. To this cause, the horizontal increase of 

 the stem, during the early part of the season, is 

 due. When the elongation of the stem has pro- 

 ceeded for a month or two, the jbrmation of Avood 

 commences, and its deposition, either in bundles 

 or layers, continues during the remainder of the 

 growing season. All must have noticed the in- 

 creased toughness of a shoot afier it is a month or 

 six weeds old. This arises from the formation of 

 woody fibre, which commences about that tiiue. 

 As this fibre is deposited under the bark, it must 

 of necessity increase the diameter of the stem; 

 and to its formation, no inconsiderable portion ol' 

 the increase in that direction, is owing. Such is 

 a general account of the growth of the stem. We 

 will now examine the subject a little more particu- 

 larly. 



As the cellular and vascular systems of plants 

 grow in ways entirely different irorn each other, 

 we will have to consider them separately. And 

 first, we will attend to the growth of the cellular 

 system. The best observations on this subject are 

 those of Mirbel, contained in two highly interest- 

 ing papers communicated to the French Academy 

 of Science, during the years 1831-2. The plant 

 on which he nriade his obijervations, was the mar- 

 chnntia polymorpha; a plant which is frequently to 

 be met within Virginia, growingin the immediate 

 neighborhood of springs. It has no regularstem, 

 and is in fiict, nothing but a green leather-like lealj 

 irregularly lobed, and springing up in wet places 

 only. His reasons for selecting this plant were, 



first, it is a cellular plant, containing no vascular or 

 woody tissue, and on this account the better fitted 

 ibr observation, when the manner of growth pecu- 

 liar to the cellular tissue was to be ascertained. 

 Second, it grows easily, requiring nothing but 

 common water, and the access of common atmos- 

 pheric air, to ensure its rapid increase ; and third, 

 its seed, or spores, as they are termed by botanists, 

 consist of a single cellule each. The common 

 pufi'-ball or snuff-box, as it is perhaps more com- 

 monly called, {bovista oiigrescens,) is a cellular 

 [jlanl. If one of these, when ripe, be pressed t)y 

 the loot, an exceedingly fine slate-colored powder 

 flies out from the opening at its summit; the grains 

 of this powder are the seeds, or spores, of that 

 [)lant; and the seeds of the marchantia, are ex- 

 actly like them, except in color. Had the botan- 

 ist the power of creating a jjlant, lor the especial 

 purpose of making observations on the growth ol 

 the cellular system, he could not have made one 

 better adapted to the purposes than the marchan- 

 tia poh/murpha. 



Some of these seeds were laid upon moistened 

 plates of glass, and placed in a warm damp room. 

 When examined, after an interval of Ibur or five 

 days, a projecting point was noticed on each of 

 ihern, which soon elongated into a slender tube. 

 This lube then swelled out at its extremity, and 

 l)ecame a second cellule, in every respect like the 

 first. Tiie newly Ibrmed cellule soon emitted a 

 lube, and this grew into a cellule ; and so the work 

 went on. The plant, at first, appeared like a knot- 

 ted cord; next, it seemed a shapeless mass of 

 green matter; and finally, became leaf-like, and 

 assumed the ap|)earance of a perlect plant. Ac- 

 cording to the observations of Mirbel, there does 

 not appear to be any fixeil point at which a cellule 

 shall give rise to another; and of course, a mass of 

 cellular tissue may increase in every direction 

 equally well. I'his is in accordance with the iact 

 already mentioned, that the cellular system of a 

 plant grows in all directions at the same Ume. 

 Cellules, in some instances, produce others at a 

 very rapid rate. Some species of mushrooms, 

 plants composed entirely of cellular tissue, have 

 been known to grow in a singlr night, from a mere 

 point, to the size of alarge irourd. In such a case, 

 if the cellules are of the medium size, they must 

 have been produceti at the average rate of 

 4,000,000,000 per hour; a rate of increase so rapid, 

 thai we could hardly believe it, did not calculation 

 show us that it must indeed be true. 



Concerning the growth of the fibro-vascular 

 system, i. e. the vascular tissue and woody fibre, 

 there has been great diversity of opinion among 

 botanists. By far the greater part of the observa" 

 lions wliich have been made, Ibr the purpose of 

 examining into this matter, have been made on 

 exogenous plants; to these, therefore, our atten- 

 tion must be principally tlirected. But yet it 

 should be remarked, we can admit no explanation 

 which does not apply to endogens, as well as to 

 exogens. The origin of the fibro-vascular sys- 

 tem, is presumed to be same in both cases ; and 

 so also Its developement, except in the single par- 

 ticular of its arrangement. 



There are certain facts respecting the produc- 

 tion of the wood, which have been established by 

 careful and oft-repeated experiments. To these 

 we will first attend. The first of these is, that 

 the wood, or at least the material of which the 



