196 THM NATURE AND WORK OF PLANTS 



red seaweeds. The top layer of water extending to 

 a depth of a hundred and fifty feet is inhabited by 

 red and some brown algse, and below this depth for 

 a short distance the red algse alone find suitable 

 conditions. Bacteria may live at depths of over half 

 a mile or in complete darkness, in the same manner 

 that mushrooms or other non-green species may live 

 in caves completely shut off from the light. 



238. Wind and plants. — The wind affects the 

 character of the stems developed, and is a very im- 

 portant factor in carrying pollen from one flower to 

 another, disseminating seeds, spores, and other repro- 

 ductive bodies. Its general direction is an important 

 factor in determining the rainfall also. 



239. Forests. — The best idea of a community 

 may be gained from the study of one as it lives in an 

 undisturbed condition, and it will be most profitable 

 to make the first observations on the subject in a 

 forest, since the relations of its members are more 

 easily determined than in some others. 



In order that the work upon this point should 

 have any great value it should be extended through- 

 out the greater part of a season, though many fea- 

 tures of interest may be made out in a single visit. 



