244 SCIENCE OF AGRICULTURE. ' Part II. 



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 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 presenting 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 augmented in height as before, and so on 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. 



1554. 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 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 failing 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 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 hill 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. 



1555. The hud, 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 what- 

 ever 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 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 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 glutinous 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 uni- 

 versally so ; for to this rule there exists a curious and singular exception in the bud of the platanus, which 

 is generated in the very centre of the base of the foot-stalk, and is not discoverable till 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 protrusion 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 elaborated 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. 



1556. Bulbs are so very similar to buds both in their origin and developement as to require no specific 

 investigation. 



1557. 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. H^nce 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 liHaceous 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 



1558. The flower and 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. Linnasus represents the pistil as originating in the pith, the stamens in the wood, and the 

 corolla and calyx in the inner and outer bark respectively : but this account of their origin, though ex- 

 tremely plausible at first sight, will not bear the test of minute examination, being contradicted by the ana- 

 tomy of the parts themselves ; particularly in the case of compound flowers. Knight in investigating the 

 organisation of the apple and pear, endeavored 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 

 termination, 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 elaborate 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 

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

 on the same subjects after the fruit was formed, the coloring matter was traced through the mass of the 

 fruit to the base of the stamina. And hence ic appears that the flower and fruit do possess the power 

 of elaborating sap for their own developement. Knight infers from the foregoing data, that the blos- 

 som 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. 



Sect. V. Anomalies of Vegetable Developement. 

 1559. A deviation from the general laws of develoj)ement is occasioned by the interven- 

 tion of some accidental cause ; or of some cause operating permanently in certain sub- 

 jects. Hence the anomaly may regard the developement either of an individual or a 

 species, and may occur either in the root, stem, branch, leaf, bud, flower, or fruit, ac- 

 cording to the circumstances in which it is placed ; or it may effect the habit, duration, 

 or physical virtues of the plant. 



