THE ROOT. 15 
which roots have to avoid it. In a room lighted by.a single 
window, place a few germinating mustard seeds on a piece of 
cotton, and let it float on water in a vessel. It will soon be seen 
that the small roots point towards the dark part of the room, while 
the stalklets bend over to meet the rays of light coming from the 
window. 
What can be the cause which determines this natural and 
invincible tendency of roots towards the interior of the earth? Is 
it that they would avoid the light because its action might be 
injurious to them? Do they seek for moisture? The two follow- 
ing-experiments will assist the reader to answer these questions. 
Place a few seeds upon a wet sponge contained in a glass tube, 
and light the apparatus from 
below. When the plant 
shall have germinated, and 
pushed out roots and root- 
lets, they will appear as re- 
presented in Fig. 16; the 
small fibres descend towards 
the lower part of the tube, 
and consequently towards 
the light, in obedience to 
towards the light that they 
take their course. 
Take a box whose bottom 
is pierced with holes, as re- 
presented in Fig. 17, and 
fill it with mould; place a 
few kidney beans in these § 
holes, and suspend the appa- imine. el 
ratus in the open air. The ae ee ees 
roots will not ascend in order to seek the humid earth. Obedient 
to the inflexible law which guides them, they will be found to 
