408 
PHYSIOLOGY. 
BOOK II. 
be inferred that several causes concur to produce the pheno- 
mena in question.’’ 
Dutrochet filled with earth a box, the bottom of which was 
perforated with many holes : he placed seed of the Kidney- 
bean in these holes, and suspended the box in the air, at 
about eighteen feet from the earth. Here the seeds, being 
placed in holes pierced through the bottom of the box, re- 
ceived the influence of the atmosphere and light from below ; 
while the humid earth was placed above them. If the cause 
of the different directions of the radicle and plumule con- 
sisted in an affinity of the former for humidity, and of the 
latter for the atmosphere, the radicle ought to shoot upwards, 
and the plumule downwards ; but this did not take place. 
The radicles, on the contrary, found their way downwards 
out of the box into the atmosphere, where they quickly dried 
up and perished; and the plumules forced their way back- 
wards into the earth. This experiment was afterwards 
modified, by increasing the quantity of earth above the seeds, 
and by some other contrivances ; but the result was always 
the same : it was uniformly found, that there was no affinity 
between the radicle and the seat of moisture sufficient to 
counteract the natural downward tendency of the roots. It 
was also inferred, that there existed no more positive affinity 
between the stems and the atmosphere than between the roots 
and water.* 
There are certain parasitic plants which strike their roots 
into the stems of other plants, and which always grow at 
right angles with the stem to which they are fixed. The 
seed of the Mistletoe will germinate in any direction, either 
upwards, downwards, or laterally. The first movement made 
by this plant consists in an extension of its caulicule, which 
derives its support from the cotyledons, and which terminates 
* Professor Schultz, however, succeeded in overcoming the tendency of 
the roots downwards and stems upwards. He planted seeds of Cab- 
bages, Mustard, and Kidneybeans in moss, and so arranged them that 
the only light they could receive was from a mirror, which threw the solar 
rays upon them from below upwards ; they sent their roots upwards, and 
their stems downwards. It would, therefore, appear that light is the great 
cause of the direction taken by the stem. 
