lo The vegetable SYSTEM. 
let into that warm place, will fhoot out leaves, and bud and blofTom 
and bear fruit even in the depth of Winter : while all the reft of 
the fame Vine is naked. Therefore even in dead Winter Sap rifes 
in the Vine ; although it has not force to fhoot out Leaves and 
Flowers till natural or artificial heat promote it. 
The great caufe of the rife of Sap from the Root is the heat of the 
air : the fall, or propulfion downward is owing to the quantity of 
moifture received by the Leaves in the evening ; which preftes down 
the Juice in the Veftels. Part of this has been exhaufted during the 
day, and the remainder being condenfed by the night’s cold does not 
fill thofe VefiTels : the quantity received above occupies the vacant 
fpace, and by its mere weight forces the reft down towards the Root; 
till the next day’s heat evaporates more from the Leaves, and raifes 
more from the Root again : and this is the caufe of every day’s motion 
in the Sap. 
There is no feafon in which there is not fome heat in the air; and 
therefore there is no time when fome Sap does not rife : the Winter 
Vine ftiews this ; and there are other proofs, which naturally have 
their place in the fucceeding Chapter. What has been called the 
Rife of Sap into the Trunks of Trees in Spring, and its Fall into their 
Roots in Winter, is in reality no more than the afcent of the Juices 
in a greater or lefs quantity, proportioned to the warmth of the air. 
In Autumn the Sap ceafes to rife in any obvious quantity, and 
through Winter the fame ftate holds : this is called the Fall of the 
Sap into the Root. But we fee there is not only no Fall, but there 
is a real Rife at that time, though little : when Spring-funs warm 
the air, and rains give abundant moifture to the earth and atmofphere, 
the Juices afcend in vifible and vaft quantities : and this is called the 
Rife of the Sap in Trees. It is needful to explain the doftrine, though 
erroneous ; for it is not in nature a Rife and Fall of thefe Juices, but 
a fwifter and more abundant, or a ftower and lefs copious afcent. 
Univerfal nature ftiews that there is no part of any Plant firm enough 
in its texture to fupport itfelf above the ground, wherein there is not, 
even in the coldeft feafons, a Rife of Sap, though it be little in 
quantity ; for when that ceafes they perifh. Vegetable bodies pre- 
lerve 
