1907] 



STEVENS— CHRYSANTHEMUM RAY BLIGHT 



245 



nearer to one end than to the other. Rarely two septa or even three 

 are present in one spore. The spores measure from 3 to 6.2 ft in 

 thickness by 10 to 20 ^l in length; 6. 2 /x by 18 /t being the usual size. 

 The spores are hyaline or very slightly greenish. In mass, as ex- 

 truded from ripe pycnidia, they appear slightly pink. The walls are 

 evidently mucilaginous, since the spores, as they are pushed from 

 the pycnidia upon the absorp- 

 tion of water, issue in worm- 

 like coils, cohering thus for 

 considerable time, though they 

 are not in visible contact. The 

 spores germinated rapidly in 

 water {fig. 5), practically 

 every spore germinating. In 

 germination the septum ap- 

 peared in all spores, and one 

 to three germ tubes protruded 

 from each cell. These tubes 

 rapidly became richly septate, 

 and the protoplasm highly 

 vacuolate. 



In sections {fig, 6) the 

 spores are seen to be borne 

 on all inner portions of the 



Fig. 6. Section of pycnidium. a, neck 

 of ostiolum. — Fig. 7. Portion of pycnidial 

 wall in section showing method of spore 



pycnidial wall except the very attachment, 

 short neck of the ostiolum, 



each spore originating singly {fig. 7) on the end of a very short stalk 

 (about 2 to 5 /x long). These sporophores are lateral branches of 

 the mycelial threads which constitute the pycnidial wall. The pyc- 

 nidium originates within the host tissue, i. e., immersed, but rapidly 

 enlarges to burst the overlying epidermis, so that the mature or even 

 half-grown pycnidium appears to be superficial. There is no special 

 aggregation of mycelium to be found below the base of the pyc- 

 nidium. 



The very young pycnidium is solid. Later a spore cavity develops, 

 though apparently no more rapidly than is necessitated by spore 

 production. In the youngest pycnidia having a spore cavity, the sur- 



