XXVII. FRIENDS AND ENEMIES OF PLANTS 



THE struggle for existence among plants is no less strenuous than 

 it is among animals. The friends and enemies of cultivated plants 

 are numerous, but in general they may be divided into the follow- 

 ing groups: (1) plant forms, (2) animal forms. Each of these 

 may again be subdivided as follows: 



L. Plant Forms 



2. Animal Forms 



I. Fungi 



II. Weeds 



I. Insects 



II. Birds 



III. Animals 



Molds 



Bacteria 



Yeast 



Annuals 



Biennials 



Perennials 



Biting or Chewing Insects 



Sucking Insects 



Predaceous Insects 



Harmful Birds 



Beneficial Birds 



Harmful Animals 



Beneficial Animals 



1. PLANT FORMS 



Fungi. We have all noticed the molds that form on bread, 

 cheese, fruit, and other articles when left exposed to the air for 

 some time. If we examine these molds with a microscope, we 

 find that they are very minute plants which do not contain chloro- 

 phyll, and this compels them to depend upon other organisms 

 for their supply of food. This food they may obtain in two ways: 

 either (1) directly from living plants and animals, or (2) from 

 organic waste products or dead bodies. The former are called 

 parasites and the latter saprophytes. Some species, however, may 

 live either as parasites or saprophytes as necessity may demand. 

 If it were not for the saprophytes, the whole earth would soon 



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