176 



SCIENCE OF GARDENING. 



Part II. 



776. The stem. The fitem, 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 tlie same manner as that of the 

 root — by additions to the extremity only, but by the intro-susception of additional particles throughout 

 its whole extent, at least in its soft and succulent state : the longitudinal extension diminishing in pro- 

 portion 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 extension 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 favorable to its elongation, because they prevent or retard its in- 

 duration ; 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, neither in height nor thickness. Such is the mode of the 

 growth and developement of the trunk of perennial and woodv 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 

 £is presenting no concentric or divergent layers, and no medullary canal, but merely an assemblage of large 

 and woody tibres, 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 pro- 

 trudes a circular row of leaves, or of fronds, which 6ro%vns 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 live 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 augmented in height as before, and so on in succession 

 as long as the plant lives, the leaves always issuing from the summit and crownuig 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. 



777. 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 a-lso a cone that 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 faUing short of the 

 centre in proportion to the lateness of its fonnation, 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 said 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 hiU — owing, as it has been thought, to the evo- 

 lution of a greater number of buds on the side that forms the obtuse angle with the soil, in consequence 

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



778. 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, are destitute of buds as well as all plants whatever growing 

 within the tropics, 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 loolc for buds ; and in them no new part is added, whether 

 proper to the leaf or flower, without the intervention of a bud. For whjcn the young shoot is produced, it 

 is at tlie same time furnished with new buds, which are again extended into new shoots in the following 

 spring ; and thus the bud is to be regarded as forming, not only the cradle but also the winter quarters of 

 the shoot, for which its coat of tiled and g'lutinous scales seems admirably well adapted. It is found chiefly 

 in the extremity, or on the surface of the young shoot or branch, and but rarely on the stem, except it be 

 at the collar where it produces suckers. It is also generated for the most part in the axil of the leaves, 

 as may be seen by inspecting the annual shoot of almost any tree at random, though not universally so ; 

 for to this rule there exists a curious and singular exception in the bud of the platanus, which is gene- 

 rated in the very centre of the base of the foot-stalk, and is not discoverable tiU after the fall of the leaf. 

 But how are the buds formed which are thus developed ? Malpighi thought they were formed from the 

 pith or cellular tissue, which the latter regarded as viscera destined for the elaboration of the sap and pro- 

 trusion of future buds. Du Hamel thinks the exterior scales of the bud originate in the interior part of 

 the bark, and Knight relates an experiment from which he thinks it follows that the buds are formed 

 from the descending proper juice. But whatever may be the actual origin of the bud, it is evident that 

 its developement does not take place except through the medium of the proper juice, which has been ela- 

 borated in the leaves of preceding buds, and originally in those of the plumelet ; as the young bud does 

 not make its appearance till the leaves of the preceding buds have expanded, and will not ultimately 

 succeed if deprived of them too soon. 



Bulbs are so very similar to buds both in their origin and developement as to require no specific inves- 

 tigation. 



779. The leaf. When the leaves burst from the expanding bud, and even long before that period, as 

 may be seen by the dissection of the bud in the winter, they are complete in all their parts. Hence it is 

 obvious that the leaf, like the young shoot, effects its final developement by means of the intro-susception 

 of new particles throughout the whole of its dimensions : and yet this law of developement is not common 

 to all leaves whatever, for the leaves of liliaceous plants extend chiefly at the point of their junction with 

 the bulb. The effect perhaps of their peculiarity of structure, in being formed of parallel tubes which ex- 

 tend throughout their whole length, without those transverse and branching fibres that constitute what 

 are called the nerves of the leaves of woody plants. 



780. The flower end fruit. When the 'flower bursts from the expanding bud, and even long before 

 that period, it is already complete in all its parts, as may be seen also by the dissection of the bud in winter. 

 LinucBus represents the pistil as originating in the pith.'the stamens in the v.-ood, and the corolla and caly.K 

 in the inner and outer bark respectively : but this account of their origin, though extremely plausible at 

 first sight, will not bear tlie test of minute examination, being contradicted by the anatomy of the partd 

 themselves ; particularly in the case of compound flowers. Kiught in investigatin,i^ the organisation (;f 

 the apple and pear, endeavoured to ascertain the origin of the several parts by tracing the organs of the 

 fruit-stalk to their termination. In the fruit-stalk he thought he could discover the pith, the central 

 tubes, spiral tubes, and tubes of the bark, together with its epidermis : and in tracing them to their ter- 

 mination, he thought the pith seemed to end in the pistils ; the central vessels in the stamens, after 

 diverging round the core and approaching again in the eye of the fruit ; and the bark and epidermis in 

 the two external skins. Hence he infers that the flower is a prolongation of the pith, wood, and bark. 

 A question of some considerable importance has arisen out of 'this subject: does the flower or fruit elabo- 

 rate sap for its own developement, or is it supplied with nourishment from the leaf? By placing small 

 branches of the apple, pear, and vine, with blossoms not expanded in a decoction of logwood, Kniglit 

 found that the central vessels were colored by the decoction. By means of a similar experiment on the 

 same subjects after the friut was formed, the coloring matter was traced llirough the mass of the fruit to 

 the base of the stamina. And hence it appears that the flower and fruit do possess the power of elaborat- 

 ing sap for their own developement. Knight infers from the foregoing data, that the blossom is nourished 

 from the alburnum, by means of the mingling of the proper juice, which the alburnum may be supposed 

 to contain with the sap in its ascent. 



