2 2o BOTANICAL GAZETTE [September 



tangle of fungous filaments is formed in its place. From the per- 

 pendicular cells arising from the stroma a cell is cut off by a trans- 

 verse septum. This cell enlarges into an oval body, the conidium, 

 which soon becomes septate. As the conidia are increasing in 

 size, the pressure on the cuticle above becomes greater and greater, 

 so that it is at length broken, leaving the margin of the exposed 

 acervulus irregularly torn (fig. i). Sometimes a central papilla 

 is present which marks the place where the cuticle will rupture. 

 At maturity the conidia are oval to elliptical and 2-celled. They 

 are hyaline and 18-25X5-6^. They may be unequally septate, 

 either straight or subfalcate, and often so deeply constricted at 

 the line of septation that the halves fall apart readily. Several 

 large granules and guttulae are normally present (fig. 3). 



Germination of conidia 



The conidia germinate within 24 hours in bean agar or in hang- 

 ing drops of water. Each of the cells may first enlarge, becoming 

 more or less spherical and vacuolate before the formation of the 

 germ tube. Frequently only one of the cells germinates by the 

 formation of one or two germ tubes (fig. 3). No formation of 

 colonies was secured in poured plates of bean agar, although the 

 fungus grows slowly when the conidia are planted on the surface, 

 forming a small, prostrate, tawny colony. Apparently growth 

 ceases as soon as the reserve food material within the conidium 

 has been utilized in the development of the short hypha. This 

 seems to occur when the hypha is 10-20 times the length of the 

 conidium and may have become branched with several septa. 

 If such conidia are cut out with as little of the surrounding medium 

 as possible and transferred to bean pods, using ordinary sanitary 

 precautions, and if the medium is spread out so as to bring the 

 germinating conidium in contact with the pod, further growth 

 may be induced. In two or three weeks small colonies are formed. 

 At first the mycelium is whitish, changing to a pinkish color and 

 becoming pale brown to blackish with age. The colonies do not 

 spread out on bean pods, but form knots of fungous tissue often 

 one-half as high as the diameter of the colony. The tissue of the 

 bean which is attacked becomes blackened in a fibrillose manner, 



