1923] 



LEHMAN — POD AND STEM BLIGHT OF SOYBEAN 123 



in clusters of 3-15 individuals, each of which possesses a long, 

 slender, black, crooked or curved beak (pi. 11, fig. 2). The 

 beak often slightly exceeds 1.5 mm. in length, possesses a diam- 

 eter of 40-60 fx, and is pierced longitudinally by a pore, which 

 presumably serves as an avenue for spore discharge. The 

 bodies of the perithecia are immersed in a stroma. This stroma 

 possesses a dense, black cortical region which covers the perithecia 

 and certain light-colored and less dense stromatic areas (pi. 13, 

 figs. 1-2). The perithecia become spherical when they develop 

 singly, but owing to the fact that several commonly develop 

 within a single stroma individuals are usually flattened in one 

 or more directions by mutual compression. Sizes, which can 

 be determined only from sections of fruiting stromata and which 

 must vary with the amount of crowding, range from 145 to 348 

 X 116 to 318 ii. Each py cnidium is separated from the stroma by 

 a wall consisting of an outer layer of dark cells and an inner 

 thicker layer of hyaline cells from which the asci arise (pi. 12, 

 fig. 2). The cells of the inner layer are larger than those of the 

 outer and the elements of both layers are arranged circum- 

 ferentially with respect to the perithecium. The asci are clavate 

 or oblone, sessile, verv numerous, vary in size from 37.2 to 50.2 



7 



and 



biseriate spores (fig. 5). The ascus wall is so thin and hyaline 

 as to be difficult to see when unstained, except at the apex where 

 it is markedly thicker and pierced by a narrow pore. Since this 

 pore penetrates a very much thickened portion of the ascus wall 

 and is of very much smaller caliber than the ascospores, it is 

 not apparent that it can well serve as an avenue of escape for 

 them. Presumably ascospores are set free by disintegration or 

 rupture of the thinner portions of the ascus wall. Ascospores do 

 not readily separate from each other in water mounts but adhere 

 in groups, probably by reason of the presence of some adhesive 

 ectoplasmic substance. Ascospores are hyaline, spindle-shaped 

 to elliptical, 2-celled, slightly or not at all constricted at the 

 septum, possess 2-4 guttulae, and measure 9.6-12.4 x 2.4-4.2 [x 

 (average 11.42 X 3.53 y.) (fig. 6). They may begin germination 

 within 4 hours in tap water at 20° C. They swell markedly in 

 thickness and nut out germ tubes from one or both cells. The 



