PLANT DISEASES 



237 



Smuts. The smuts cause the black powdery masses that are 

 often to be seen upon corn, oats, and other grains. They are 

 particularly fond of mem- 

 bers of the grass family. 

 Their spores germinate in 

 spring soon after the seeds 

 of the plants which they 

 infect begin to grow. Get- 

 ting into the plant through 

 the stomata or through a 

 break in the tissues, they 

 grow with the growing 

 plant until seeds begin to 

 be formed. At this point 

 they fill up the young seed 

 with their own tissues and 

 soon produce a mass of 

 exceedingly minute black 

 spores that float away to 

 infect other plants, or that 

 cling to the seeds of the 

 plants upon which they 

 grow, and are transported 

 with them. The seeds of 

 oats are often treated with 

 formalin or hot water to 

 destroy the spores before 

 they are planted. 



Rusts. The rusts cause 

 rusty brownish or blackish 

 patches on the leaves and 

 stems of many plants. Fields of wheat or corn, late in the 

 season, will furnish good examples, and others may be found 

 in asparagus beds. Often the wheat rust is so abundant as to 



FIG. 175. Anthracnose of beans 



From Duggar's " Fungous Diseases of 

 Plants" 



