248 



REDUCED ASCOMYCETES 



92A. Order g. Exoascales or Peach Curl. — This group in- 

 cludes a small number of parastic fungi that are especially destruc- 

 tive to peach and plum trees, causing distortion of the leaves 

 and fruit, known as leaf curl and bladder plum (Fig. 159). There 

 is apparently no trace of a reproductive process, the mycelium 

 spreading through the leaf develops directly a rudimentary 

 hymenium of numerous asci beneath the cuticle, which is finally 



Fig. 159. Fig. 160. 



Fig. 159. A branch from peach tree, showing the distortion of the leaves 

 caused by the fungus, Exoasctis. 



Fig. 160. Section of a leaf showing numerous cells rupturing the cuticle 

 and developing into asci, as. 



ruptured by their growth (Fig. 160). The ascospores are dis- 

 charged into the air by the bursting of the asci and carried by 

 the wind to other plants. The damage in the United States to 

 peach trees alone is estimated at $2,000,000 to $3,000,000 

 annually. 



93. Order h. Yeast or Saccharomycetes. — These fungi are 

 unicellular plants with little suggestion of mj^celial growth. 

 Ordinarily they consist of rather oval cells which multiply rapidly 

 by a budding suggestive of conidia formation in preceding orders 

 (Fig. 161). The ncAV cells that push out from the side of the 

 mother cell readily drop off, but in rapid growth they may 

 remain attached in chains (Fig. 161, D). Under certain condi- 

 tions, as the exhaustion of the food supply, the cells become 

 transformed into asci and the contents of each cell rounds off 

 into one or more ascospores (Fig. 161, jE). The ascospores are 



