LEA 
An oblique Leaf ( Obliquum ) is when the bafe of the 
Leaf regards the fky, and the fummit the horizon. 
An indexed or incurved Leaf (Inflexurn) is one which 
grows in form of a bow, turning its point toward the 
fcaik again, fig. 94. 
sidpreffwm , is when the difk of the Leaf approaches 
near the italic. 
An erect Leaf ( Ereffum ) is one fo fttuated as to make 
a very acute angle with the italic, fig. 95. 
Patens , is when the Leaf does not make fo acute an 
angle with the italic as the former, and yet does not 
itand horizontal, fig. 96. 
An horizontal Leaf ( Horizontale ) is one which fcands 
perfectly at right angles with the italic, fig. 97. 
A reclined Leaf ( Reclinatum ) is one whofe fummit is 
lower than the bafe, fig. 98. 
A rolled Leaf ( Revclutnm ) is one whole upper part 
is rolled downward, fig. 99. 
A dependent Leaf ( Pependens ) is one whofe fummits 
point to the earth. 
A rootingLeaf ( Radicans ) is one which puts out roots. 
A floating Leaf ( Natans ) is one which floats on the 
furface of the water, 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 botaniits diftinguifh them, and alfo their pofi- 
tion, both in regard to the other parts of the tree, or 
plant, and that of the earth, we fhall next proceed to 
their ftruffure and ufes •, for thefe were not defigned 
by the wife Creator only for ornament, but they are 
of more important ufe in vegetation, and are as va- 
rioufly conftrufted in their feveral parts, as their fe- 
veral ufes for which they are defigned. 
Some plants have very thick fiefhy Leaves, whofe 
pulpy iubftance is always moift thefe are fuch plants 
as naturally grow upon dry barren rocky places, and 
for the moil part are natives of warm countries ; and 
as they perfpire very little in comparifon of moil other 
plants, they are adapted to grow in fuch places where 
they can receive very little nourishment from the 
earth. Moft of the Leaves of thefe plants have a thin 
compadl fkin over their furface, with very fmall mi- 
nute pores, whereby the defcending moifture is thrown 
off, which, if admitted into the iubftance of the Leaves, 
or ftalks, would in a very fhort time caufe a mortifi- 
cation, and deflroy the plant. 
The Leaves of all thole trees and ilirubs which 
continue their verdure all the year, have alfo a thin 
compadi fkin or cover over their furfaces, as is eafily 
difcovered by macerating them in water, in order to 
feparate the parenchyma from the veftels of the leaves, 
which cannot be effected in any of thefe Evergreens, 
till the thin parchment-like cover is taken off; thefe 
trees and fhrubs are found, by experiment, to imbibe 
and perfpire but little in the fame fpace of time, when 
compared with the deciduous trees and fhrubs ; and 
it is principally owing to this clofe covering, as alfo 
to the fmall proportion of moifture contained in their 
vefiels, that they retain their verdure, and continue 
through the winter on the trees. The nutritive 
juices of thefe plants always abound more or lefs with 
an oily or terebinthinous quality, which fecures them 
from the injury of froft, fo that many of thefe ever- 
green trees are adapted to grow in the coldefc parts of 
the habitable world. 
In all the Leaves of trees and plants which I have exa- 
mined, there are two orders of veins or nerves, one 
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 fo pafs through them, which thofe of 
the upper furface would not ; thefe two orders of 
veins are inofculated at feveral places, but not fo 
clolely conneded, 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 loft 
enough to feparate eafily from the veins without tear- 
ing them, 
LEA 
Thefe two laminse, or orders of veins, are fuppofed 
to be deftined for different purpofes ; the upper lami- 
na is thought to be air-vefifels, or trachai, through, 
which the perfpiring matter is protruded, and by which 
the air is infpired ^ that thefe are pores through which 
that iubftance paffes, which is thrown out of the plants, 
is pretty evident for the clammy Iubftance which is 
commonly called honey-dew, is always found flicking 
to the upper furface of Leaves, from whence many 
have fuppofed that this fubftance fell from above, and 
lodged upon the Leaves in the night. This is the 
Manna which is colleded from Afh-trees in Calabria, 
and from the Alhagi in Perfia, &c. and is no other 
than the nutritive juices, or a fubftance. feparated 
from that, which iffues 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 be deftined 
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 flop and detain the rifing vapours, and tranfrnit 
them to the inner veffels ; and where the ftrudlureof 
the Leaves are different, it is found by experience, 
that their fundlions alter ; for thofe Leaves, whofe 
upper furfaces are garnilhed with down or hairs, 
are found to be the receivers and conveyers of 
the moifture, and not the under ones, as in the 
other plants. 
If the furfaces of thefe Leaves are altered, by reverfing 
the branches on which they grow, the plants are flop- 
ped in their growth, until the foot-ftalks are turned, 
and the Leaves recover their former pofition. This 
Shews how neceffary it is to fupport all thofe weak 
Shoots of plants, which are naturally difpofed for up- 
right growth, and that either twine about the neigh- 
bouring trees for fupport, or that put out clafpers, 
by which they take hold of whatever trees or plants 
grow near them, and are thereby fuppoited ; and, on 
the contrary, how abfurd is that practice of tying 
up the fhoots 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. 
This is one of the great fundtions for which the Leaves 
of trees and plants are defigned ; but, befides this, 
there are others of equal importance to the well-being 
of plants and fruits ; the firft is that of the foot- 
ftalks of Leaves nourifhing and preparing the buds of 
the future lboots, which are always formed at the 
bafe of thefe foot-ftalks, and during the continuance 
of the Leaves in perfect health, thefe buds increafe 
in their magnitude, and, in the deciduous trees, 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- 
maining, yet the buds will decay, or not arrive to 
their proper fize, for want of that nourifhment which 
is conveyed to them from the Leaves ; fo that when- 
ever trees are diverted of their Leaves, or thofe 
Leaves are cut, or otherwife impaired, though it may 
in either cafe happen when the buds may be nearly 
formed ; yet if it is before the foot-ftalks feparate 
naturally from the branches, the future fhoots will be 
weakened in proportion to the time when this is done ; 
therefore, as from all the experiments which have been 
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 diverted of 
their Leaves, or their Leaves have been eaten, or cut, 
during their growth, the plants have been remarkably 
weakened thereby. This fhould teach us not to pull, 
or cut off the Leaves of trees, or plants, on any 
account, while they retain their verdure or are in 
7 X health, 
34! 
