the Developement of the seminal Germ. 259 
were placed above it; and the plumelet, on the contrary, by 
ascent, even when the access of air was possible only from below. 
If the points of the roots or fibres became horizontal or even 
ascending in the latter part of the experiment, it is to be recol- 
lected that germination was then past; and that the extremities 
of vegetating roots are often found to deviate from the line of 
descent in quest of a more fertile portion of soil. 
- But although the insufficiency of Dr. Darwin’s hypothesis 
should even be admitted, there remains yet another hypothesis to. 
combat. For Mr. Knight, whose meritorious labours in Phyto- 
logy are too well known to this Society to stand in need of any 
encomium from me, has still more recently attempted to account 
for the descent of the radicle upon the old but revived principle 
of gravitation, strengthened, as he no doubt mes: by the fol- 
lowing results of experiment. 
Beans, which were made to germinate after being fastened in 
all positions to an upright and revolving wheel, that performed 
150 revolutions in a minute, uniformly directed the radicle out- 
wards from the centre, and the plumelet inwards to the centre: 
and beans that were so fastened to a horizontal and revolving 
wheel, performing the same number of revolutions in the same 
space of time, uniformly protruded their radicles obliquely out- 
wards and downwards, and their. plumelets obliquely inwards and 
upwards*; which effects Mr. Knight regards as resulting from 
the centrifugal influence of the wheel's motion counteracting that 
of gravitation, which is consequently, in his opinion, and in the 
natural position of the seed, the cause of the radicle's descent. 
This conclusion, if it has not been adopted by botanists in 
general, has been adopted at least by Sir Humphry Davy, one 
of the most illustrious chemists and phytologists of the present 
* Nichol. Journ. xiv. 410 
VOL. XI. 2M times, 
