DEVELOPMENT OF PLANTS 



227 



other corn plants by means of their basidiospores (Fig. 164, B). 

 In other cases, the teleutospores germinate in the spring, infest- 

 ing the seedlings. This appears to be always the case in the 

 destructive wheat, rye, oats and barley smuts. Infection only 



f 



FIG. 163. 



FIG. 164. 



FIG. 163. A common smut, Ustilago, transforming the kernels of corn 

 into sooty black pustules. 

 FIG. 164. The formation and germination of the spores of a smut: 



A, the formation of the spores from the mycelium in the kernel of corn. 



B, germination of a spore and the appearance of the basidiospore. 



takes place when the spores come in contact with the seed. Con- 

 sequently, in these cases, the fungus can more readily be fought 

 by treating the seed with some fungicide as formaline and copper 

 sulphate. 



96. Order c. Agaricales or Mushrooms and Toadstools. 

 This is the most familiar group of the basidiomycetes and its 

 12,000 odd species are commonly referred to as mushrooms and 

 toadstools. These fungi are largely saprophytes, living upon 

 the humus in the soil and upon decaying wood. Several of the 

 .genera are exceedingly destructive to trees and cause great loss 

 to' the lumber industry. In the majority of cases, the fungus 

 appears unable to attack the living portion of the tree and only 



