MICHIGAN ACADEMY OF SCIENCE. 281 



the disease produced, and the fungus again isolated. There is no ques- 

 tion of the causal relationshij) of tlie fungus to this disease. 



DESCRIPTION OF THE CAUSAL ORGANISM. 



The causal organism is a fungus characterized by dark septate 

 mycelium, wliich ramifies through the host tissue, and gives rise to short, 

 erect conidiophores which bear single, dark brown, muriform spores. 

 These are the characters of the genus Macrosporium of the Fungi Imper- 

 fecta 



The specific characteristics of the spores, conidiophores, and mycelium 

 are as follows : 



Spores : 



The spores are muriform, sarcina-like (packet) in shape, constricted 

 in the middle, and usually separated at that point into two distinct parts 

 by a cross wall. These parts are subdivided by transverse and longi- 

 tudinal partition walls which are ordinarily not as thick as the outer or 

 the medium division wall. A spore viewed from the point of attachment 

 shows a small circular scar where it was attached to the conidiophore. 

 The contents of the spore consist of a dense, hyalin protoplasm witli 

 many globules (mostly oil) which ooze out when the spore is crushed. 

 The color ranges from hyalin in the very young to dark brown or 

 fuliginous in the older spores. Occasionally a yellow-colored spore may 

 be seen fully developed in form and size, but such a spore darkens with 

 age. The surface of the spore is smooth and no roughenings or prom- 

 inences of any sort have ever been seen. The size ranges from 

 22.4-37.7 X 19.1-27.4 microns, with an average of 28.9x22.4 microns. 



Conidiophores : 



The conidiophores are usually borne at an approximate right angle 

 to tlie mycelium which gives rise to them. They are dark brown to 

 fuliginous in color, and on the host are 23.2-74.7 microns long by 5.0-5.1 

 microns wide. The tip cell which is darkest in color is swollen and 

 flattened, resembling in shape the knob of a pestle. The two or three 

 cells nearest tlie tip of the conidiophore have a more homogeneous and 

 finely granular contents than the basal cells. These basal cells frequently 

 bear knobs (Plate XIII, Fig. 2). Sometimes on the host, but rarely in 

 culture, the tip cell of the conidiophore instead of at once giving rise 

 to a spore, sends out another cell which is similar to it in shape and 

 structure. The spore is then produced upon this secondary tip cell 

 (Plate XIII, Fig. 3). 



Mycelium : 



The young mycelium in culture is more or less vacuolate and finely 

 granular in structure, sparingly septate, branched, and 2.5-4.0 microns 



