L 



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turning its point toward the 

 difk of the Leaf approaches 



E A 



Thefe two laminjE, or order-s of veins, are fuppofed 

 to be dcftined for different purpofcs ; the upper lami- 

 na is thought to be air-veiTcls, or trach:^, through 

 which the perfpiring matter isprotruded, and by which 

 the ar is infpired •, that thefe are pores throuo-h which 

 that i'ubftance pafTes, which is thrown out of the plants, 

 is pretty evident •, for the clammy fubftance which is 

 coaimonly called honey-dew, is always found {lickin-T 

 to the upper furface of Leaves, from whence many 

 have fuppofed that this fubitance fell from above, and 

 lodged upon the Leaves in the night. This is the 

 Manna which is collefted from Alli-trces in Calabria, 

 and from the Alhagi in Perfia, &c. and is no other 

 than the nutritive juices, or a fubftance feparated 

 from that, which ilTues from the pores of the Leaves, 

 and is concreted on the furface of the Leaves by the 

 cold air •, but whenever this is found in quantity 

 upon the Leaves, it is a fure fign of a difeafed plant. 

 The lower lamina of veins are fuppofed to bedeftined 

 for another purpofe, which is that of receiving, pre- 

 paring, and conveying the moifture imbibed from the 

 rifing vapours of the earth, by which trees and plants 

 are greatly nourifhed ; and for this ufe we fee how 

 differently the two furfaces are formed ; the upper 

 one is commonly fmooth and lucid, and the under is 

 frequently covered with hairs, or a foft down, the bet- 

 ter to ftop and detain the rifing vapours, and tranfmit 

 them to the inner veffels ; and where the ftrufture of 

 the Leaves are different, it is found by experience, 

 that their functions alter; for thofe Leaves, whofe 

 upper furfaces are garniflied with down or hairs, 

 are found to be the receivers and conveyers of 

 rioufly conftrufted in their feveral parts, as their fe- I the moifture, and not the undertones, as in^.the 

 veral ufes for which they are defigned. ( other plants, '^ • ; ;yx', ' ' / 



If the furfaces of thefe Leaves are altered, by reverfing. 

 the branches on which they grow, the plants are ftop- 

 ped in their grov/th, until the foot-ftalks are turned, 

 and the Leaves recover their former pofition. This - 



An oblique Leaf {Obliqutim) is when the bafe of the 

 Leaf regards the fky, and the fummit the horizon. 

 JSvi inficxed or incurved Leaf {Infiextan) is one which 

 grows in form of a bow 



ll;ilk again, fig. 94. 



jidpr^Jp^m^ is when th 



nea- the ftalk. 



An ereft Leaf {Ere^um) is one fo fituated as to make 



a very acute angle with the ftalk, fig. 95. 



patens^ is. when the Leaf does not make fo acute an 



angle with the ftalk as the former, and yet does not 



ftand horizontal, fig. 96. 



All horizontal Leaf {Horizonlale) is one which ftands 



pcrfeftly at right angles with the ftalk, fig. 97. 



A reclined Leaf {Reclinatum) is one whofe fummit is 



lov/er than the bale, fig. 9S. 



A rolled Leaf {Revolutum) is one whofe upper part 



is rolled downward, fig. ^(), 



A dependent Leaf {Depcndens) is one whofe fummits 



point to the earth. 



A vootmcr'L.^dS {Radicans) is one which puts out roots. 



A floating Leaf {Natans) is one which floats on the 



furface of the w^ater, as the Water Lily, &c. 

 Demerfum^ is ufed to exprefs a Leaf funk below the 

 furface of the water. -. ' - ■ , 



Having explained the feveral forms of Leaves, by 

 which botanifts diftinguifti them, and alfo their pofi- 

 tion, both in regard to the other parts of the tree, or 

 plant, and that of the earth, v/e ftiall next proceed to 

 their ftru6lure and ufes -, for thefe were not defigned 

 by the wife Creator only for orharrient, but they are 

 of more important ufe in vegetation, and are as va- 





Some plants have very thick flelhy Leaves, whofe 

 pulpy fubftance is always moift ; thefe arefuch plants 

 as naturally grow upon dry barren rocky places, and 

 for the moft part are natives of warm countries \ and 

 as they perfpire very little in comparifon of moft other I fliews how neceffary it is to fupport all rhofc weak 



. t 



plants, they are adapted to grow in fuch places where 

 they can receive very little nourilhment from the 

 earth. Moft of the Leaves of thefe plants have a thin 



ftioots of plants, which are naturally diipofed for up- 

 right growth, and that either twine about the neigh- 

 bouring trees for fupport, or that put out clafpers. 



compaft Ikin over their furface, with very fmall mi- by which they take hold of whatever trees or plants 



nute pores, whereby the defcending moifture is thrown 

 off, which, if admitted into thefubltance of the Leaves, 

 or ftalks, would in a very ftiort time caufea mortifi- 

 cation, and deftroy the plant. ' ' * "' ^ 

 The Leaves of all thofe trees and fhrubs which 

 continue their verdure all the year, have alfo a thin 

 compa6l fkin or cover over their furfaces, as is eafily 

 difcovered by macerating them in water, in order to 

 feparate the parenchyma from the veffels of the leaves, 

 which cannot be effefted in any of thefe Evergreens, 

 till the thin parchment-like cover is taken off; thefe 

 trees and ftirubs are found, by experiment,*to Tmbibe I- 

 and perfpire but little in the fame fpace of time,' when 

 compared with the deciduous trees and fhrubs ; arid 

 \t is principally owing to this clofe covering, as alfo 

 to the fmall proportion of moifture contained in their 

 veffels, that they retain their verdure, ahJ continue 

 through the winter on the trees. The nutritive 



grow near them, and are thereby fupported ; and, on 

 the contrary, how abfurd is that practice of tying 

 up the (hoots of thofe plants which are naturally 

 difpofed to trail upon the ground ; for, in both thefe 

 cafes, nature is reverfed, and confequently the growth 

 of both forts of plants is greatly retarded. 



-i^t- ■-■' * 



This is one of the great fundtions for which the Leaves 

 of trees and plants are defigned'; butV befides this, 

 thefe are others of equal importance to the well-being 

 of plants and fruits • ' the firft is that of the foot- 

 ftalks of Leaves nouriftiing and preparing the buds of 

 the future flioots, which are always formed at the 

 bafe of thefe foot-ftalks,' and during the continuance' 

 of the Leaves in perfeft health, th^efe budsjijc^eafe; 

 in their magnitude, and, in the deciduous tVees,^ are 

 brought to maturity before the foot-ftalks feparate" 

 from the buds in autumn ; but if by accident the 

 Leaves are blighted, or if the entire furface of the 

 .Leaves are cut off, and the foot-ftalks are left re- 

 mainingr yet the buds will decay, or_ not arrive to 

 their proper Xize, for want of that nouriftiment which 

 is conveyed to" them from the Leaves ; fo that when- 

 ever trees "are diverted of their Leaves, or thofe 

 In all the Leaves of trees arid plants which I have exa- I * : Leaves are cut, or otherwife impaired, though it may 

 mined, there are two orders of veins or nerves', one > in either cafe happen when the buds may be nearly 





..^* 



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juices of thefe plants always abound more or lefs with 

 an oily or terebinthinous quality, which fecures them 

 from the injuiy of froft, fo that many of thefe ever- 

 green trees are adapted to grow in the coldeft parts of 

 the habitable world.' ;■ "^ ' 



«/# ► .— 



belonging to each furface -, and I have generally ob- 

 ferved, that the lower lamina or under fide of the Leaf, 

 had the ramifications larger, and were capable of ad- 

 mitting a liquid to pafs through them, which thofe of 

 the upper furface would not -, thefe two orders of 

 veins are inofculatcd at feveral places, but not fo 

 clofely conne6ted, but that they may be eafily fepa- 

 rated, after they have been macerated in water a pro- 

 per time, for fome Leaves require a' much longer 

 time than others, to' render the parenchyma ioft 

 enough to feparate eafily from the veins without tear- 



ing them. 



- ; 



formed •, yet if it is before the fopt-ftalks feparate 



naturally from the branches,^ the future ftioots will be 



weakened in proportion to the time when this is done ; 



therefore, as from all the experiments which have beea 



made in order to know how ferviceable the Leaves 



of trees and plants are to their well-being, it has been 



found, that where the plants have been divefted of 



their Leaves, or their Leaves have been eaten, or cut, 



during their growth, the plants have been remarkably 



weakened thereby. ' This fliould teach us not to pull,/ 



or cut off the Leaves of trees, or plants,' on an;^'-' 



account, while they retain their verdure 'or are in ' 



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