1816.] On the upright Growth of Vegetables. 451 
leled to the circulation of the blood. The blood is impelled 
through every part of the body by no mechanical attraction or 
chemical affinity; but by a principle, sw generis, connected with 
animal life, and which, though its action may be increased by sti- 
mulants, and diminished by narcotics, cannot be communicated by 
any exertion of human power. The analogy between vegetable and 
animal life has certainly in some instances been carried beyond the 
bounds of sober reason, but no one can refuse assent to the existence 
of a connexion between these two orders of being, indicating a 
common principle in their organization. The circulation of the 
blood, therefore, produced by the irritability of the heart, leads us 
to ascribe the circulation of the sap to a similar organization in the 
vegetable ; and as the examination of the sap vessels in trees does 
furnish evidence of a construction suited to such a purpose, we 
have good reason to conclude that this is indeed the true theory of 
that phenomenon. 
The origin of that prejudice which would lead us to ascribe to 
the circulation of the sap the perpendicular growth of the vegetable 
will be found in the inaccuracy of the expression ascent of the sap. 
We now see that, instead of concluding that the germen is forced 
upwards by the ascending sap, we have better reasons to conclude 
that the sap ascends, because the plant stands perpendicular. Being . 
absorbed by the roots, its course, if it flows at all, is necessarily 
upwards in an upright stem. But it flows in all directions, and 
with equal force in a trailing as in an upright plant. Like the cir- - 
culation of the blood, which was destined to proceed with an equal 
course, unaffected by the position of the animal, the flow of the 
sap, intended to nourish all the parts of the plant, was made to 
depend ona principle altogether unconnected with those laws which, 
however powerful or extensive in their operations, are all essentially 
connected with the centre of gravity. Instead of ascent, therefore, 
we ought to adopt the expression circulation of the sap; and by the 
introduction of a term implying an indefinite direction, we shall 
extricate the question from that confusion which so invariably 
results from inaccurate descriptive expressions. 
But if there be no principle ‘as yet discovered to which, by an 
internal upward pressure, we can ascribe the full solution of the 
problem, the conviction that the cause is still to be found in the 
ascent, or descent of something connected with the plant, leads us 
to examine the external operations of vegetation, and in particular 
the constant and copious evaporation which seems essential to the 
existence of that process. 
The quantity of water which is absorbed and evaporated by diffe- 
rent plauts has been the subject of many experiments, It has been 
gravely stated that the improvements in agriculture,‘ by increasing 
the quantity of vegetables in this island, have so much increased the 
quantity of vapour as to have materially deteriorated the climate. 
Without adopting such an unpleasant opinion as this, we may safely 
credit the statements of well-informed naturalists when, from their 
