92 DISEASES OF THE SWEET PEA 



compound microscope. When grown in 

 pure culture, however, they are plainly 

 visible as colonies of aggregate individ- 

 uals. 



Insects are divided into two classes : one 

 class derives its food by sucking the plant 

 juices and is known as "suckers" ; the other 

 class chews and eats solid parts of roots, 

 stems, foliage, or blossoms, and is known 

 as "biting." All insects undergo certain 

 changes (metamorphosis), beginning as 

 larvae and ending as adult beetles, bugs, 

 or butterflies. Not all animals which are 

 parasitic on plants are insects, as, for ex- 

 ample, the eel worm. The latter belongs 

 to the Arthropoda of the Animal Kingdom, 

 its body being composed of many segments 

 with no legs. 



Red spiders and mites, likewise plant 

 parasites, are not insects. These belong 

 to the Arachnida or true spiders. Books 



