244 SCIENCE OF AGRICULTURE. Part II. 



obtained the same result, deduced from it also the same conclusion. We may regard it, then, as certain, 

 that the mode of the elongation of the root is such as is here represented, though in the progress of its 

 developement, it may affect a variety of directions. The original direction of the root is generally perpen- 

 dicular, in which it descends to a considerable depth if not interrupted by some obstacle. In taking up 

 some young oak trees that had been planted in a poor soil, Du Hamel found that tlie root had descended 

 almost four feet, while the height of the trunk was not more tiian six inches. If the root meets with an 

 obstacle, it then takes a horizontal direction, not by the bending of the original shoot, but by the sending 

 out of lateral shoots. The same effect also follows if the extremity of the root is cut off, but not always ; 

 for it is a common thing in nursery gardens to cut off' the tap-roots of drills of seedling oaks, without 

 removing them, by a sharp spade, and these generally push out new tap-roots, though not so strong as the 

 former. When a root ceases of its own accord to elongate, it sends out lateral fibres which become 

 branches, and are always the more vigorous the nearer they are to the trunk ; but the lateral branches of 

 horizontal roots are the less vigorous the nearer they are to the end next the trunk. In the former case, 

 the increased luxuriance is perhaps owing to the easy access of oxygen in the upper divisions ; but, in the 

 latter case, the increased luxuriance of the more distant divisions is not so easily accounted for, if it is not 

 to be attributed to the more ample supply of nutriment which the fibres meet with as they recede from 

 the trunk, particularly if you suppose a number of them lying horizontally, and diverging like the radii of 

 a circle. But the direction of roots is so liable to be affected by accidental causes, tliat there is often but 

 little uniformity even in roots of the same species. If plants were to be sown in a soil of the same density 

 throughout, perhaps there might be at least as much uniformity in the figure and direction of their roots, 

 as in those of their branches; but this will seldom happen. For if the root is injured by the attacks of 

 insects, or interrupted by stones, or earth of too dense a quality, it then sends out lateral branches, as in 

 the above cases ; sometimes extending in length, by following the direction of the obstacle, and some- 

 times ceasing to elongate, and forming a knot at the extremity. But where the soil has been loosened by 

 digging or otherwise, the root generally extends itself to an unusual length ; and where it is both 

 loosened and enriched, it divides into a multiplicity of fibres. This is also the case with the roots of 

 plants vegetating in pots, or near a river, but especially in water. Where roots have some considerable 

 obstacle to overcome, they will often acquire a strength proportioned to the difficulty : sometimes they 

 will penetrate through the hardest soil to get at a soil more nutritive ; and sometimes they will insinuate 

 their fibres into the crevices even of walls and rocks, which they will burst or overturn. This of course 

 requires much time, and does much injury to the plant. Roots consequently thrive best in a soil that is 

 neither too loose nor too dense; but as the nourishment which the root absorbs is chiefly taken up by 

 the extremity, so the soil is often more exhausted at some distance from the trunk than immediately 

 around it. Du Hamel regards the small fibres of the root, which absorb the moisture of the soil, as being 

 analogous to the lacteals of the animal system, which absorb the food digested by the stomach : but the 

 root is rather to be regarded as the mouth of the plant, selecting what is useful to nourishment, and 

 rejecting what is yet in a crude and indigestible state ; the larger portions of it serving also to fix the 

 plant in the soil, and to convey to the trunk the nourishment absorbed by the smaller fibres, which, 

 ascending by the tubes of the alburnum, is thus conveyed to the leaves, the digestive organs of plants. 

 Du Hamel thinks that the roots of plants are furnished with pre-organised germs, by which they are 

 enabled to send out lateral branches when cut, though the existence of such germs is not proved ; and 

 affirms, that the extremities of the fibres of the root die annually, like the leaves of the trunk and 

 branches, and are again annually renewed ; which last peculiarity Professor Willdenow affirms also to be 

 the fact, but without adducing any evidence by which it appears to be satisfactorily substantiated. On 

 the contrary. Knight, who has also made some observations on this subject, says, it does not appear that 

 the terminating fibres of the roots of woody plants die annually, though those of bulbous roots are found 

 to do so : but the fibres of creeping plants, as the common crowfoot and strawberry, certainly die annu- 

 ally, as do those of the vine. 



1582. The stem. The stem, like the root, or at least the stem of woody plants, is also augmented in 

 width by the addition of an annual layer, and in length, by the addition of an annual shoot bursting from 

 the terminating bud. Is the developement of the shoot issuing from the stem effected in the same man- 

 ner also ? The developement of the shoot from the stem is not effected in the same manner as the 

 developement of that from the root, by additions to the extremity only, but by the introsusception of 

 additional particles throughout its whole extent, at least in its soft and succulent state : the longitudinal 

 extension diminishing in proportion as the shoot acquires solidity, and ceasing entirely when the wood 

 is perfectly formed, though often continuing at the summit after it has ceased at the base. The exten- 

 sion of the shoot is inversely as its induration, rapid while it remains herbaceous, but slow in proportion 

 as it is converted into wood. Hence moisture and shade are the most favourable to its elongation, because 

 they prevent or retard its induration ; and hence the small cone of wood which is formed during the 

 first year of the plant's growth increases no more after the approach of winter, either in height or thick- 

 ness. Such is the mode of the growth and developement of the trunk of perennial and woody plants, to 

 which there exists a striking exception in the growth of the trunk of palms. Their internal structure 

 has been already taken notice of as possessing no concentric or divergent layers, and no medullary canal, 

 but merely an assemblage of large and woody fibres, interspersed without order in a pulp or parenchyma, 

 softer at the centre, and gradually becoming harder as it approaches the circumference. When the 

 seed of the palm tree germinates, it protrudes a circular row of leaves, or of fronds, which crowns the 

 radicle, and is succeeded in the following year by a similar row issuing from the centre or bosom of the 

 former leaves, which ultimately die down to the base. This process is continued for four or five years 

 successively, without exhibiting as yet any appearance of a stem, the remaining bases of the leaves or 

 frond forming by their union merely a sort of knob or bulb. At last, however, they constitute by their 

 union an incipient stem, as thick the first year as it ever is after ; which in the following year is aug- 

 mented in heighth as before, and so in succession as long as the plant lives, the leaves always issuing 

 from the summit and crowning the stem, which is a regular column, but decaying at the end of the year, 

 and leaving circular marks at the points of insertion, which furrow the surface of the plant, and indicate 

 the years of its growth. 



1583. The branches, in their mode of growth and developement, exhibit nearly the same appearances 

 as the trunk from which they issue. They originate in a bud, and form also a cone which consists of pith, 

 wood, and bark ; or rather they form a double cone: for the insertion of the branch into the trunk 

 resembles also a cone whose base is at the circumference, and whose apex is at the centre, at least if it is 

 formed in the first year of the plant's growth, or on the shoot of the present year ; but falling short of the 

 centre in proportion to the lateness of its formation, and number of intervening layers. Branches in their 

 developement assume almost all varieties of position, from the reflected to the horizontal and upright; 

 but the lower branches of trees are found to be generally parallel to the surface of the soil on which they 

 grow, even though that surface should be the sloping side of a hill, owing, as some have thought, to the 

 evolution of a greater number of buds on the side that forms the obtuse angle with the soil, in conse- 

 quence of its being exposed to the action of a greater mass of air. 



1584. The bud, which in the beginning of spring is so very conspicuous on the trees of this country as to 

 be obvious to the most careless observer, is by no means common to all plants, nor to plants of all 

 climates; shrubs in general, and annuals universally, as well as all plants whatever growing within 

 the tropics, are destitute of buds, the leaf being in them immediately protruded from the bark. It is only 

 in the woody plants of cold climates, therefore, that we are to look for buds ; and in them no new part is 

 added, whether proper to the leaf or flower, without the intervention of a bud. For when the young 

 shoot is produced, it is at the same time furnished with new buds, which are again extended into new 



