DEVELOPMENT OF PLANTS 



209 



will doubtless be greatly improved. It contains bacteria, and if 

 not fresh will seriously interfere with the quality of the bread. 



84. Order b. Exoascales or Peach Curl. This group includes 

 a small number of parasitic fungi that are especially destructive 

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

 fruit, known as leaf curl and bladder plum (Fig. 140). Numer- 



FIG. 140. FIG. 141. 



FIG. 140. A branch from peach tree, showing the distortion of the 

 leaves caused by the fungus, Exoascus. 



FIG. 141. Section of a leaf showing numerous cells rupturing the cuticle 

 and developing into asci, as. 



ous asci are developed from the mycelium beneath the epidermis, 

 which is finally ruptured by their growth (Fig. 141). The asco- 

 spores are discharged 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. 



85. Order c. Aspergillales or Blue-green and Brown Fungi. 

 This group includes perhaps the most widely distributed and 

 familiar examples of the fungi. They occur as blue-green or 

 brown moulds upon almost any organic matter, forming a deli- 

 cate mycelium from which are developed numerous erect hyphae. 

 In the common blue mould, Penicillium, these erect hyphae are 

 broom like (Fig. 142, B) and the spores are formed from the 

 tips of the branches very much after the manner of the budding 

 of the yeast cells. The tip of a branch buds out into a spherical 

 cell that is finally cut off from the stalk, thus forming the spore 

 15 



