1907] 



STEVENS— CHRYSANTHEMUM RAY BLIGHT 



243 



the presence of a rather coarse, much branched mycelium that is 

 easily recognized by its septa, which are numerous and stand out 

 with an especially striking clearness 

 {fig^ 2). In the humid region between 

 the flowers in the head, the mycelium 

 becomes aerial, forming a loose floccose 

 weft, visible to the naked eye. In the 

 pith cavity of the blighted receptacle 

 a similar profuse mycelial develop- 

 ment occurs; while on old specimens/ 

 in culture dishes, pycnidia were also 

 found identical with those which de- 

 veloped in the pure cultures to be 

 described later {fig, j). Only one 

 fungus was seen and no bacteria • 

 whatever w^ere visible. 



ISOLATION 



Diseased ray flowers were removed 

 with sterile forceps and thrown upon 

 solidified pea agar in Petri dishes, 

 several to each dish. Similarly, with 



Fig. 2. — ^Normal h}'phae, mature, 

 showing septation with slight con- 



aseptic precautions, bits of the wood striction; also the mode of branching 



and bark from diseased peduncles, 



stems, and from the inside of the receptacle 

 were plated. Each of these cultures, 25 or 

 more in number, plated on November 18, 

 resulted within 24 hours in pure colonics, all 

 alike, of a fungus with a mycelium identical 

 in appearance with that seen in diseased 



tissue. 



Fig. 3. — Surface view 

 of pycnidium showing 

 reticulation. 



THE FUNGUS 



The colonies grew with remarkable rapidity 



and remained sterile until five days old. 

 Pycnidia were found then in the oldest portions of a colony upon 

 one of the plates. They were amber color, as seen with the two- 

 thirds objective and transmitted light approaching no. 30 of Sac- 



