the wheel, the radicles always taking a course 
diametrically opposite to that taken by the germs, 
and consequently pointing as much below as the 
germs pointed above the plane of the wheel’s 
motion. 
These facts afford a rational solution of this 
curious problem, respecting which different phi- 
losophers have given such different opinions ; some 
referring it to the nature of the sap, as De la 
Hire, others, as Darwin, to the living powers of 
the plant, and the stimulus of air upon the leaves, 
and of moisture upon the roots. The effect is now 
shown to be connected with mechanical causes ; 
and there seems no other power in nature to which 
it can with propriety be referred, but gravity, 
which acts universally, and which must tend to 
dispose the parts to take a uniform direction. * 
If plants in general owe their perpendicular di- 
rection to gravity, it is evident that the number 
of plants upon a given part of the earth’s circum- 
ference, cannot be increased by making the 
surface irregular, as some persons have supposed. 
Nor can more stalks rise on a hill than on a spot 
equal to its base ; for the slight effect of the at- 
traction of the hill, would be only to make the 
plants deviate a very little from the perpendicular. 
Where horizontal layers are pushed forth, as in 
certain grasses, particularly such as the florin, 
* Fig. 1. represents the case in which the horizontal wheel 
performed 250 revolutions. 
Fig. 2. represents the form of the experiment when the ver- 
tical wheel was made to perform 150 revolutions in a minute. 
