THE ACORN AND ITS GERMINATION 19 
minate—a fact which suggests that some profound mole- 
cular or chemical changes have to be completed in the 
living substance of the cells before further activity is 
possible. We have other reasons for believing that 
this is so, and that, until certain ferments have been 
prepared in the cells, their protoplasm is unable to make 
use of the food materials, and consequently unable to 
initiate the changes necessary for growth. 
Sooner or later, however, and usually as the tempera- 
ture rises in spring, the embryo in the acorn absorbs 
water and oxygen, and swells, and the little radicle elon- 
gates and drives its tip through the ruptured investments 
at the thin end of the acorn, and at once turns downward, 
and plunges slowly into the soil (fig. 3). This peculi- 
arity of turning downwards is so marked that it manifests 
itself no matter in what position the acorn lies, and it 
is obviously of advantage to the plant that the radicle 
should thus emerge first, and turn away from the light, 
and grow as quickly as possible towards the centre of 
the earth, because it thus establishes a first hold on the 
soil, in readiness to absorb water and dissolve mineral 
substances by the time the leaves open and require 
them. 
The two cotyledons remain enclosed in the coats of 
the acorn, and are not lifted up into the air; the de- 
veloping root obtains its food materials from the stores 
in the cells of the cotyledons, as do all the parts of the 
young seedling at this period. In fact, these stores in 
the cotyledons contribute to the support of the baby 
c 2 
