16 THE VEGETABLE WORLD. 
descend through the holes in the box into the dry air, in which — 
they will soon be dried up. It is not moisture therefore that 
roots seek after. 
It has been suggested that the action of gravitation would take 
Fig. 17.—Box experiment. 
some part in the guidance of the roots. This is, in fact, the 
apparent tendency of the following experiments. 
Beans have been made to germinate when placed on the circum- 
ference of an iron or wooden wheel surrounded with moss, so as 
to maintain the moisture of the seeds, and holding little troughs 
full of mould, open on two sides (Fig. 18); the wheel being put 
in motion in a vertical direction by a current of water and made to 
describe many revolutions in a minute. In consequence of this rotary 
movement, producing the particular force known in mechanics as 
centrifugal force, the action of gravitation being as it were anni- 
hilated, and the sprouting seed removed from its influence, and 
subjected to centrifugal force only ; now see what occurs. The small 
rootlets, which in ordinary circumstances would be directed upwards, 
that is to say, in a direction inverse to the action of gravitation, 
