THE ACORN AND ITS GERMINATION. 19 



spicuous change ; and in any case it requires a period of 

 rest before the presence of the oxygen of the air and 

 the moisture of the soil are effective in making it ger- 

 minate a fact which suggests that some profound mo- 

 lecular 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 pre- 

 pared 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 temper- 

 ature rises in spring, the embryo in the acorn absorbs 

 water and oxygen, and swells, and the little radicle 

 elongates and drives its tip through the ruptured in 

 vestments at the thin end of the acorn, and at once 

 turns downward, and plunges slowly into the soil 

 (Fig. 3). This peculiarity of turning downward is so 

 marked that it manifests itself no matter in what posi- 

 tion 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 pos- 

 sible towards the center 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 inclosed 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 



