440 THE ECOLOGY OF PLANTS. 



In the latter case the trees have a less perfect leaf -mosaic, and 

 while affording protection to the undergrowth admit a larger 

 amount of light. The difference in the amount and variety 

 of undergrowth in a dense Beech wood and in a well-lighted 

 Oak or Birch wood is very striking (Figs. 180, 181) ; even 



Fig. 180. A light mixed wood (chiefly Birch), showing dense urictergrowtn ol 

 Bramble, etc. 



under a small clump of Beeches, or a single large Beech, there 

 are very few plants. The struggle for existence in a wood 

 is largely a struggle for light. 



In woods the air temperature is slightly below that of the 

 open country, and the daily temperature changes are less 

 pronounced. Owing largely to the shelter from wind, the air 



