424 



FUNGOUS DISKASKS OK PLANTS 



teleutospores with long, gelatinizing pedicels (Fig. 206). These 

 teleutospores germinate immediately. Three promycelia often 

 arise from a spore, each through a germ pore situated near the 

 septum between the two cells. The promycelium may form four 

 sporidia in the usual manner, and these sporidia 

 cannot reinfect the cedar. They may apparently 

 be borne long distances by the wind. Moreover, 

 they are produced during the season when young 

 leaves and fruits are abundant on the apple, 

 quince, and such plants. Falling upon the con- 

 genial host, the spore immediately germinates, 

 and infection is secured. In time the rust stage 

 of the fungus appears. This stage consists of 

 spermogonia and ascidia. It is then perhaps mid- 

 summer, and the abundant aecidiospores return 

 the fungus to the conifer host, where in time a 

 gall or a deformity is again produced. 



The rust spots on the pomaceous hosts appear 

 at first as clear yellow or orange areas, slightly 

 thickened or raised. Soon a papillate appearance 

 indicates the presence of the spermogonia or pyc- 

 nidia, which are all of a characteristic, simple 

 type. The aecidia follow in a brief period on the 

 under side of the leaf, or covering large areas on 

 the fruit (Fig. 205). The aecidium (rcestelia) is an 

 organ of some length, appearing cylindrical or 

 jug-shaped after emergence. A circular orifice 

 is developed, and the peridium breaks into a 

 characteristic margin, sometimes fimbriate. The spores, which 

 are produced in chains, break apart when mature. They also 

 germinate immediately. 



Control consists primarily in the removal of the cedars, if that 

 is practicable. Attention should also be paid to the resistance of 

 varieties of apples grown. It is, moreover, of some value to spray 

 with the standard Bordeaux mixture at about the time of ripening 

 of the teleutospores. 



FIG. 206. 6'jMAvo- 

 x/'oK.-t\t;ri:.\r MA- 

 CRO PUS: TI.I.I i - 

 TOSP 



