IV 



CAUSES OF PLANT DISEASES 



69 



animals. They are frequently classified with fungi, the 

 great group of plants to which they bear the closest 

 resemblance. They do not contain chlorophyll, and 

 therefore cannot manufacture starch like the green 



FIG. 36. Tree attacked by mistletoe. (Photo by H. H. York.) 



plants, but are compelled to live upon organic com- 

 pounds. 



They are unicellular and very small and can be 

 studied only with high-power microscopes. Some are 

 spherical and known as cocci, others short and rod-like 



