92 



Forest Club Annual 



in diameter, reddish-brown above with a lighter colored, shaded 

 border, paler below. Pycnidia upon the lower side of the spots, 



minute (80 microns in diameter), 

 globose, numerous, filled with el- 

 liptical hyaline spores 2x0.5 mi- 

 crons. On the leaves of Acer 

 glabrum from northwest Nebraska. 



Septoria 



In Septoria the pycnidia occur 

 on brownish or whitish deadened 

 areas in the leaf as in Phyllosticta- 

 The disease:! tissue is sharply 



Fig. 19. Septoria. a. Habit 

 upon the leaf. b. Pycnidium 

 \ery much enlarged. All 

 highly magnified. 



defined so that the spots are 

 very conspicuous in contrast 

 to the green surrounding tissue. 

 The pycnidia are sub-cuticular 

 as in the former genus, and 

 they are also very similar to 

 those of Phyllosticta in shape. 

 But in Septoria the spores are 

 rod-shaped or thread-like, and 

 many septate and hyaline. Thus 

 the nature of the spore is seen 

 to be the greatest difference be- 

 tween this genus and the pre- 

 ceding one. See fig. 19. 



Septoria acerella Sacc. 



Discolored spots angular, 

 .nainly conspicuous on the up- 

 per side of the leaf, small, 



Fig. 20. Leptostroma on 

 Gleditsia showing pycnidia. 

 Actual size. 



