B O T A N Y. 



ble the arrangement of vessels. (See PI. LX VI I. Fig. 3.) 

 " ) (Jxsalpinus fancied tliat the sole use of leaves was to 

 """^ shelter the fruit and blossoms from excessive heat or 

 cold. This use they certainly fulfil to a certain ex- 

 tent ; hut th. iv are K .ides certain great and import- 

 ant uses, which shall he discussed in their proper 

 places. All the particular details respecting the form 

 and structure of leaves, are to be found in Grew's 

 works, in which the most faithful statements are af- 

 forded, not only of whatever is connected with this 

 subject, but also on every point of vegetable anatomy. 

 Leaycs are seminal, radical, or those attached to 

 the branch. Their mode of attachment is not always 

 the same, (see Part I. Sect. ii. Art. 31.) and it has 

 therefore been selected as a distinctive character. To 

 determine this peculiarity, it is necessary to examine 

 the base with great care, as the attachment is always 

 at that part of the leaf. Most generally stalks (Part 

 I. Sect. ii. Art. 11.) are the means employed, and 

 tlu-y vary considerably in form and dimensions. 



It has been already observed, that buds produce 

 leaves, which, in the early stages of their existence, 

 are rolled up, or folded in such a manner, as to occu- 

 py the smallest possible space ; and it is worthy of 

 notice, that this arrangement is uniformly the same 

 in individuals of the same species, and in the species 

 of the same genus. In this dormant condition they 

 remain in,, the bud until the vital principle is roused 

 to activity, by the return of the season best suited to 

 its operations : In our temperate climate, that season 

 is spring, when nature seems to awaken from the 

 sleep of winter. In some cases the flowers precede 

 the leaves ; but more commonly the reverse of this 

 takes place. In tropical regions, vegetation does not 

 appear to undergo this cessation, and new leaves are 

 formed apparently without the regular intervention of 

 buds, at the coolest period of the year. If it be re- 

 collected, that plants of the same species, in similar 

 situations, will develope their leaves at the same time, 

 and that plants of different species perform this func- 

 tion at very different periods, it appears at least pro- 

 bable, that a particular temperature is requisite for 

 each species. Adanson paid much attention to this 

 subject, and he has determined that the same tempe- 

 rature is required by the same plant on all occasions, 

 whether the season be early or late. On this fact he 

 instituted a comparison between the periods of ger- 

 mination and of producing leaves, by which the far- 

 ir.jr may regulate the sowing of his different crops. 

 Linnaeus obtained many facts relative to this point 

 in Sweden, and has treated it with his usual vi- 

 gour, in the AmcEtiitntes Academica: It would 

 be worth while to carry on, in every country, an ex- 

 tensive suite of examinations of this kind. Men of 

 intelligence, accustomed to accuracy of observation, 

 would be requisite ; and there is no doubt that the 

 result would be no less interesting to the philosopher, 

 than useful to the practical cultivator. It has been 

 proposed to name the table of observations thus form- 

 ed, the Calendar of Flora, which, though a little 

 fantastic, would answer sufficiently well. 



After the bursting of the buds and the first de- 

 velopement of the leaves, their gradual increase and 

 perfection proceed with various rapidity, according 

 to the nature of the plant itself, and according to 



the favourableness of the climate or season. During Vegetable 

 the progressive stages, it may be conceived that num- l' ii y ; >' ol "i;y- 

 berless changes are momentarily taking place in the ~ ~ 

 component parts of the leaf itsi-lf, as well as in the 

 circulating juices that pass through that organ : but 

 exclusive of those changes, there are some living pro- 

 perties peculiar to the leaf, so singular and wonder- 

 ful, that we shall premise our account of the parti- 

 cular functions, by a sketch of them. 



The first and most remarkable of all the living Irritability 

 phenomena of the leaf, is its IRRITABILITY, which 

 has been noticed in a preceding Section. This pro- 

 perty is interesting in all its relations, whether con- 

 sidered as forming a link between the two animated 

 kingdoms, or as explanatory of all the apparent ac- 

 tions of the plant. By irritability, we mean that Definition, 

 power in living bodies which, when acted upon by 

 certain other powers, will induce an action of those 

 parts in which it is inherent, and in this sense we 

 must be understood whenever we make use of this 

 term in the course of the present article. Leaves, General 

 particularly those that are compound, exhibit this laws, 

 phenomenon in a very singular degree ; sometimes in 

 the regular course of nature, and sometimes when 

 placed in novel situations for the purposes of experi- 

 ment. Each plant that displays a marked irritability, 

 appears more especially affected by particular sti- 

 muli ; so that some which exhibit the most singular 

 degree of this quality, are perfectly unaffected by any 

 stimulus, except that which seems to have been ap- 

 propriated by nature to attain the especial object : a 

 proof to our minds, that we have only a faint glimpse 

 of the purposes of the Great Author of Nature, or 

 even of those general laws by which He regulates 

 the operation of animated beings. It is rendered p art acte(l 

 tolerably certain, by the experiments of Calandrini, O n. 

 that the display of irritability in the natural course 

 f vegetation is owing, if not in all, at least in many 

 cases, to the leaf itself, and not to the foot-stalk. 

 This gentleman suspended vine leaves by a thread, 

 after having previously separated them -from the vine 

 itself, and he found that they turned round to the 

 light as they would have done had they not been se- 

 parated from the stem. Leaves will become accus- j n fi l]entc 

 tomed to particular stimuli, and will cease to be af- O f habit 

 fected by them. M. Gerardin relates, that the cele- 

 brated Desfontaines convayed in a carriage a plant of 

 the Mimosa sensiliva, which is so remarkable for 

 this property, as to derive its specific name from it, 

 to a considerable distance in a coach, and that the 

 first effect of the violent motion of the carriage was 

 to induce the closing of the leaves, but after some 

 time, no collapse of the leaves took place, although 

 the motion continued with equal violence. 



Gerardin records a most singular fact relative to. sj nen i ar 

 the Minton,: sensitiva, which he considers inexplicable, exception. 

 " I have seen," says he, " in one of my public ex- 

 ercises, in the central school of Vosges, and many 

 were present besides myself, a young lady, who did 

 not know this plant, on whom several of those plea- 

 santries, so agreeable in society, were; passed, that 

 was urged to place her hand on it; after some hesi- 

 tation, but being assured that no evil would result 

 from the experiment, she passed her hand with some 

 force over the plant which I had presented to her, 



