VEGETABLE STRUCTURE. 
183 
The Radical Leaves of Plants are thofe which rife immediately 
from the Root, with their own Footflalks ; w'hicii have no connediion 
with the Flowering Stalk of the Plant, but precede it in order of time ; 
ferve for its firft growth, fupport and nouriflunent, till it has Leaves of its 
own 5 and then decay, and periHa utterly. 
These Leaves are always compofed of three fubflances; a Rind, a Blea, 
and Clufters of Veffels. Sometimes they have alfo an outer Bark over the 
Rind, bat not always. The Rind of their Foothalk is a continuation of 
the inner Rind of the Root, which expanding over the Leaves thcmfelves, 
becomes a common Membrane: when they have an outer Rind, that alio 
is produced fimply by a continuation from the outer Bark of the Rcot. 
The Blea of thefe Leaves is alfo fimply continued from the Blea of th.e 
Root : and the Veffels rife from thofe of the Conic Clufiers of the Root; tlio’ 
not by plain continuation, but by a peculiar kind of vafcular Bafe, 
The office of thefe Leaves is to evaporate during the day a great part 
of that Moifture w'hich the Roots draw from the ground, after its nou- 
rifhing Juices have been feparated by the feveral Glands; and in the cooF 
of evening, and during night, to receive from the ah a quantity of moif- 
ture replete with the like nourifhmcnt for the Plant, which is to be fe- 
creted in the fame manner. They ferve alfo to keep up a perfedl commu- 
nication between the Root and rifing Stalk ; for the Veffels which form 
their Ribs, are fent from the Conic Clufters of the Root, which commu- 
nicate with the Fleftiy Shell from wdience the new Stalk rifes ; and they 
return again into it. This is a fadt which has not been enough known. 
No Veffel of the Leaf terminates in the Leaf ; they all run back into the 
Footftalk, and purfue their courfe to its Bafe, returning there upon them- 
felves again. This forms what we have called a fecondary fyftem of Cir- 
culation, dependant on that primary one in the Flefli. 
Seed Leaves agree with Radical Leaves in this Strudfure : it has been 
fhewn in the courfe of the Veffels of the Seed Leaves of the Radifli, and 
may be feen diftindtly in the Radical Leaves of the generality of Plants. 
In thofe of the Bloody Dock, this return, and the inofculations of the 
Veffels, are very evident, becaufe the Ribs are thick, and highly coloured : 
but of all Plants the Colocasia fhews it moft diftindtly. Jn the Radi- 
cal Leaves of that Plant, the main middle Rib, and the feveral fide Branches, 
terminate in a large purple line, which runs round the whole circumfe- 
rence of the Leaf j and in the middle fpace between each pair of fide 
Ribs, runs a delicate returning Veffel : this takes its origin from the Cord 
which furrounds the Leaf, and empties itfelf by innumerable Branches, 
into 
