. 254 The Rev. Parrick Kerry on 
to the excess of the specific gravity of the juices of the radicle 
beyond that of the juices of the plumelet, which in their progress 
upwards were supposed to be reduced by the process of elabora- 
tion to a light vapour. But this is by no means known to be the 
fact; or, rather, it is known not to be the fact, and consequently 
forms no ground of argument. Others have attributed it to the 
respective action of the sun and earth ; the former attracting the 
leaves and stem, and the latter attracting the root. But it hap- 
pens rather unfortunately for the conjecture, that the phzenome- 
non is exactly the same even when seeds are made to vegetate in 
the dark. Du Hamel repeated the experiment in a dark room, and 
obtained the same result as in the light. The influence of the 
sun was then transferred to that of the air, which was thought to 
have some peculiar attraction for the plumelet that the earth had 
not. But the attraction of the air was just as mysterious as that of 
the sun, and the subject as much in want of elucidation as before. 
In this stage of the inquiry Dr. Darwin, of philosophical and 
poetical memory, undertook the explication of the phenomenon, 
and endeavoured to account for it chiefly upon the principle now 
specified, the radicle being presumed to be stimulated by mois- 
ture, and the cotyledons and plumelet by air, and each to be 
. hence elongated in the direction of its exciting cause*, which is 
precisely the direction assumed by the radicle and plumelet re- 
spectively in the actual developement of the seminal germ ; the 
. former descending into the earth, as being excited by. the action 
of moisture, and the latter ascending into the — as 
being excited by the action of the air. 
This hypothesis is, no doubt, sufficiently ingenious, but is by 
no means to be regarded as a satisfactory solution of the difficulty. 
. For at this rate all cotyledons, germinating in their natural soil, 
* Phytolog. sect. ix. 
P 
ER 
