170 



FARMERS' REGISTER. 



[No. S 



as the trumpet-creeper, (bignonia radicansS) It is 

 a iiict, worthy of remark, with respect to twining 

 stems, that whilst stems of different species twine 

 in different directions, the stems of the same spe- 

 cies always twine in the same direction. The 

 stem of the pole-bean always twines to the left ; 

 the same is true of the stem of the hop, (hximulus 

 lupuhts.) It may be well to recollect this, as it is 

 olten necessary in gardeninfj to start the young 

 stem around its support. If either of the plants 

 just mentioned, be started to the right, it will soon 

 throw itself down ; or, if confined in any way, 

 eo as to be forced to make a turn or two in that 

 direction, it becomes puny and of little account. 

 This is a wise provison of nature ; as most twin- 

 ing plants send forth several stems to twine around 

 the same support ; if they did not all twine in the 

 same direction, they must, of necessity, frequently 

 cross each other. Whilst all were young, they 

 would lie close to the body of the support ; but as 

 they increased in size, the inner ones, in conse- 

 quence of their growth, would tend to force the 

 outer ones further out ; whilst the outer ones, for 

 the same reason, would tend to bind the inner 

 ones closer to the support. In this way they would 

 either cut each other off, or at least, impair the 

 freedom with which their sap could circulate. 



The grape, passion-flower, &c., fasten them- 

 selves to their support by means of a class of or- 

 gans, termed tendrils. These are slender thread- 

 like organs, capable of coiling spirally, and thus 

 fixing themselves to neighboring bodies. Ten- 

 drils sometimes proceed from the extremity of the 

 leaf, and appear to be mere prolongations of the 

 mid-rib, as in the sweet-pea, (/a/Aynis ndoratus,) 

 but more commonly from the stem itselfj as in the 

 gourd, (^cucurbita lagcnaria.') When these ten- 

 drils first appear, they are straight, and not coiled 

 aa we generally see them ; but beinrr possessed of 

 a contractile power, the moment they touch any 

 euitable support, their end hooks around it, and thus 

 fastened, they go on coiling themselves until they 

 are firmly fixed'their places. If the tendrils of the 

 gourd-vine be left to develope itself fully, without 

 being suffered to touch any other support, it will 

 be perfectly straight. If it be then brought in 

 contract with a rod, or any suitable support, the 

 moment its end touches the rod it will hook around 

 it ; if the rod be now moved towards the vine, the 

 tendril will not unhook, as might be supposed, 

 but will coil itself further around. In this way a 

 Btraight tendril may be made to coil itself through- 

 out almost the whole of its length, in the course of 

 a few minutes. 



Notwithstanding the great diversity of form, 

 and external appearance, which stems present, 

 their internal structure is remarkably uniform. 

 Those of flowering plants, are all made up of 

 tubes, woody-fibre and cellules, arranged in one 

 or the other' of the two following ways. First, 

 the tubes and woody fibre are arrangedin concen- 

 tric bands, having the cellular tissue, in part, pack- 

 ed in between them, and in part forming lines 

 cutting them at right angles, and radiating fl-om 

 the axis of the stem. Such stems increaseby the 

 regular addition of new layers on the outside of 

 the old wood ; and are thence termed exogenous 

 stems, or growers outwardly, as the name im- 

 ports. This is the structure of all of the trees, 

 and most of the smaller plants of this country. 

 Second, the tubes and woody fibre are disposed in 



bundles throughout the stem ; the intersticea be- 

 ing filled up with cellular tissue. The stems hav- 

 ing this structure do not increase in diameter, after 

 they are once fairly formed, but only in solidity. 

 This they do by the addition of new bundles of 

 tubes and woody fibre internally. Hence they 

 have received the name of endogens, or growers 

 inwardly. An example of a stem of this kind is 

 furnished by the Indian corn (zea mays). Many 

 of the large trees of tropical countries are con- 

 structed on this plan. These two classes of stems 

 will have to be considered separately. As the 

 former is by far the most common in this country, 

 as well as the best understood, we will commence 

 with that. 



In a transverse section of an exogenous stem 

 of one year's growth, the three following paria 

 are easily distinguishable from each other. U't, the 

 pith, occupying the centre of the stem ; 2d, a 

 band of wood surrounding the pith ; and 3d, the 

 bark or external covering of (he stem. 



The pith, or medulla, as it is termed by botan- 

 ists, isacylindric column of spongy cellular tissue, 

 commencing at the collar or neck of the plant, ex- 

 tending throughout the whole length of the stem, 

 and terminating in the buds. Its size, as com- 

 pared with that of the whole stem is variable. In 

 the white-heart hickory (carya tomentosa^ of one 

 year's growth, the diameter of the pith, is about 

 one-sixth of that of the stem ; in the elder ( sam- 

 hiicus jviger^ of the same age, it is two-thirds. 

 Herbs and young shoots, in proportion to their 

 bulk, have much more pith than trees ; indeed 

 this must necessarily be the case, as the column 

 of pith when once formed, never increases in size. 

 In neivly formed parts, the pith is juicy, being fill- 

 ed with the ascending sap ; in the same stem, 

 when old, it is dry, colorless, and very light. At 

 first, it \s an unbroken column, and in most plants 

 it continues to be so ; in some instances, however, 

 it is torn into separate pieces by the ra|)id elonga- 

 tion of the stem ; as may be seen in the stem of 

 the walnut (juglanf: nigra, ) and still more dis- 

 tinctly in that of the poke-weed (phytolacca de- 

 candra.) Respecting the office of the pith, many 

 singular opinions have been entertained. Amongst 

 others, which it would be useless lor me to men- 

 tion at lensth, some of the earlier botanists ima- 

 gined its oflice to be similar to that of the nervous 

 system in animals. This opinion was based upon 

 a fancied resemblance, in structure and position, 

 to the spiral marrow of animals. If the pith does 

 indeed possess the properties of a nervous sys- 

 tem, some plants are much more highly favored 

 in this particular, than even the higher orders of 

 animals. So far as we know, the principal use of 

 the pith, is to transmit nourishment to the buds 

 during the earlier periods of theirgrowth. When 

 no longer filled whh the juices of the plant, it is 

 apparently useless. It seems to be a temporary 

 provision, to enable the young plant in the first 

 instance, and the young bud afterwards, to grow 

 until their own systems of vessels are fully formed ; 

 after that is accomplished, it is thrown aside. Such 

 temporary provisions are by no means uncommon 

 in nature. 



If we examine the band of wood, which sur- 

 rounds the pith, we will notice that it is cut at 

 right angles, by a number of their vertical plates, 

 sent out in every direction, from the pith to tha 

 circumference of the stem. These are called mc- 



