THE PLANT AND ITS ENVIRONMENT 



171 



Living Organisms. — The cnvironinontal factors which we 

 have been discussing thus far are all lifeless ones. Of the utmost 

 significance to the plant are also the living organisms with which 

 it is surrounded. Its relations to this organic environment 

 are many and varied. First in importance is the struggle for 



Fig. 90. — A parasite. The dodder (Cu.^ruta) parasitic on an herbaceous plant. 

 Note the absence of chlorophyll and the reduction of leaves to scales. 



survival which is taking place continually between living things. 

 No plant exists by itself, reacting only to the inorganic factors 

 which surround it. It is competing with its neighbors for water, 

 for nutrient materials, for sunlight, for insect visitors, and for 

 other necessities. It is prej^ed upon by parasitic plants. It is 

 devoured or destroyed by animals of all kinds. Only the vigorous 

 and the fortunate succeed, and they are few compared with 

 the hosts which fail and die. 



