BOTANY. 



Vegetable 



' 'V 



Internal 

 structure. 



Origin. 



Period of 



iurmatiou. 



Develope- 



nient. 



Functions. 



that form an exception to this observation, can thrive 

 indifferently in any climate ; so that the rule holds in 

 all distinct case?. The scales are considered by ma- 

 ny as imperfect leaves. 



The internal structure of buds is said not to differ, 

 in any respect, from that of the plumule, previous to 

 its being detached from the seed. Some have fan- 

 cied, that they have seen the rudiments of every part 

 of the tree concealed in the bud ; and Mr Ferbcr ex- 

 presses high delight at having observed in the buds 

 of the Hcpntica and Pedicularis -vitlgaris, yet lying 

 in the ground, the perfect plant of the future year. 

 We are much inclined to question the accuracy of 

 such very minute observers, and, of course, are more 

 willing to impute any errors to optical deception, 

 than any wish to mislead. 



The bark and the pith have been generally consider- 

 ed the sourceof the buds ; but the ingenious experiments 

 of Mr Knight have set aside both of these hypotheses, 

 and have established, as far as the present state of the 

 science will permit, the doctrine, that they derive their 

 origin from the alburnous portion of the tree. This 

 gentleman first shewed, that they do not originate in 

 the pith or bark ; and also, that Duhamel's opinion 

 of pre-existing germs being their source, is at least 

 improbable. He then proves, that the " alburnous 

 vessels at their termination upwards, invariably join 

 the central vessels ; and that these vessels, which ap- 

 pear to derive their origin from the alburnous tubes, 

 convey nutriment, and probably give existence to new 

 buds and leaves. It is also evident, from the facility 

 with which the rising sap is transferred from one side 

 of a wounded tree to the other, that the alburnous 

 tubes possess lateral, as well as terminal orifices : and 

 it does not appear improbable, that the lateral as well 

 as the terminal orifices of the alburnous tubes, may 

 possess the power to generate central vessels, which 

 vessels evidently feed, if they do not give existence to 

 the reproduced buds and leaves. And therefore, as 

 the preceding experiments appear to prove, that 

 the buds neither spring from the medulla nor the 

 bark, / am muck inclined to believe that they are ge- 

 nerated by central vessels, which spring from the late- 

 ral orifices of the a/bunions tubes." By interrupt- 

 ing the circulation in the alburnum, buds may be ar- 

 tificially produced ; and nature has provided means for 

 their reproduction, in those cases where they may 

 have been accidentally destroyed. Several curious 

 facts on this subject may be obtained by an examina- 

 tion of the potatoe, which, like other tuberous roots, 

 are studded with them. 



Buds of all kinds are formed about midsummer ; 

 after which it has been stated, " that there seems to 

 be a kind of pause in vegetation for about a fort- 

 night." Darwin imagined that a store of nourishing 

 matter is collected during that period, which pro- 

 duces the apparent pause. The season of develope- 

 ment is most usually that of the spring, when nature 

 seems to delight in new products : it is then that the 

 buds are evolved, and enter upon the important func- 

 tions they are destined to perform. Nothing, how- 

 ever, is known of these functions beyond the general 

 result. Branches, leaves, and flowers are produced 

 by btids ; but what are the particular operations by 

 these effects are induced > The answer is ea- 



sy, but unsatisfactory. Buds, transpire, and ill all Vegetal 

 likelihood produce the same chemical changes on. the ^T' 1 

 atmosphere with the other parts of the plant. '^ 



SECT. V. On Leaves. 



LEAVES constitute so large a portion of plants, are Leaves, 

 so very universal, and perform such important offices 

 in the vegetable economy, that it will be necessary 

 to enter at some length into an account of them. In- 

 dependent of the various valuable purposes to which, 

 they are applicable, there are few vegetable produc- 

 tions more truly beautiful. The richness and variety of 

 their colours, their admirable disposition on the 

 branches, the variety of their forms, and even the 

 shortness of their existence, contribute to rank them 

 among the most interesting objects of Nature. When, 

 however, we examine into and learn that these appa- 

 rently simple and beautiful organs are subservient to 

 the great end of vegetable existence, our more plea- 

 surable sensations are converted into those of admira- 

 tion and wonder. 



Leaves are distinguished by the various external Extern*'* 

 characters of their form and substance. ( Part 1 . form. 

 Sect. ii. Art. 31.) That there is an immense variety 

 in all these respects is sufficiently known ; but the 

 manner in which these diversities are induced is ob- 

 scure and unintelligible. There can be no uoubt that 

 all these varieties of form in leaves are destined to an- 

 swer some great and important end, although we have 

 not been able to penetrate into the recesses of Na- 

 ture : in some, however, the objects are so beautiful, 

 and at the same time so obvious, that the most indif- 

 ferent observer must be struck with them in an emi- 

 nent degree. Thus, we find that the thick succulent leaf 

 is most common in those countries, where a scarcity 

 of water prevails ; and, on the contrary, the thin dry 

 leaf exists where water is abundant, and the exhala- 

 tions go on more freely. The most common colour 

 of leaves in the healthy state is green in all its shades. 

 There are exceptions to this many being red, brown, 

 white, scarlet, yellow, and even black. On this topic 

 some further observations shall be made in the latter 

 part of this Section. 



Leaves are composed of cuticle, parenchymatous internst 

 substance, vessels of different kinds, and are common struct 

 ly covered with a transparent varnish. The inferior 

 surface, in general, is rougher, and of a less dark 

 green than the superior one. The cuticle abounds in 

 pores, although they are not discernible under ordi- 

 nary circumstances. Mirbel indeed says, that the 

 largest pores are on the under surface in the leaves of 

 trees, bui on both the under and upper surfaces of 

 herbaceous plants. These pores answer a twofold 

 purpose, as we shall afterwards see. The pulpy 'i :t- 

 ter affords the colour to the leaf. The vessels, be- 

 sides the pores, are continuations of the central ves- 

 sels, which convey the sap to the leaves, and those 

 vessels that reconvey that fluid to the bark and al- 

 burnum. This structure may be well seen, either 

 by gently removing the external covering, and by mi- 

 croscopical observations, or by macerating the leaves, 

 and then separating the pulpy matter from the vascu- 

 lar system. Vtry commonly natural skeletons of 

 leaves are to be found, and they beautifully illustrate 



