94 
UPWARD GROWTH OF THE HEAD, AND [.Part II. 
Dutroche", 
Knight, Davy, 
&e., think that 
gravity directs 
the growth both 
of the head and 
the roots of 
trees. Experi¬ 
ments in proof. 
So far light would appear to be the principal 
agent in directing the growth of the heads 
of plants. Yet the majority of physiologists 
attribute the direction of the growth both of the 
head and of the roots of plants to gravity. 
Among the number are Dutrochet, Knight, and 
Sir Humphrey Davy, men for capacity and 
clearness of intellect matchless among physi¬ 
ologists. I will therefore go at length into two 
experiments of Dutrochet and Knight, the con¬ 
clusions drawn from which in favour of gravity 
have been enforced by Sir Humphrey Davy. 
Dutrochet found that if beans, in a state of ger¬ 
mination, were planted in holes through the 
bottom of a box filled with earth, the stems 
grew upward from the light into the earth, and 
the roots downward towards the light into the 
air; and the plants perished when they ceased 
to derive nutriment from their seeds. 
Early in March* 1844, I made experiments 
similar to those of Dutrochet, with results which, 
if at first they resembled, finally differed very 
widely from, those elicited by this eminent and 
most acute physiologist. And in considering 
these results, I think I shall be able to explain 
why the beans in Dutrochet’s experiment died. 
I placed various seeds on the surface of large 
