1923] 



LEHMAN — POD AND STEM BLIGHT OF SOYBEAN 117 



enlargement results in a subspherical fruiting body which slightly 

 elevates the overlying epidermis and sclerenchyma layer and 

 later ruptures these tissues by the development of a short beak. 



The pycnidia on leaves are less numerous, more scattered, 

 and more nearly isodiametric in cross-section than on pod and 

 stems. The stromatic thickening of the wall is also less con- 

 spicuous on leaves and no definite beak is formed. 



The majority of the pycnidia are simple, 1-chambered struc- 

 tures. However, individuals with 2 chambers are not infre- 

 quently found (pi. 9, fig. 8). The 2-chambered type apparently 

 results from development of two simple individuals in very 

 close contact. The contiguous walls may remain intact or may 

 partly disappear at the time of spore formation, leaving only 

 vestiges of the partition attached to the side walls. Each cham- 

 ber, however, develops its own ostiole so that a 2-chambered 

 pycnidium has 2 places of escape for spores. 



The wall bounding the pycnidial cavity may be divided into 

 2 portions: an outer layer whose cellular elements are arranged 

 circumferentially with respect to the pycnidium, and an inner, 

 lighter portion of irregular-cellular arrangement from which the 

 slender hyaline conidiophores arise (pi. 9, fig. 9). The cells 

 of this outer layer are thin-walled, light brown in color, and 

 indistinctly discernible at the base of the pycnidium, but, as 

 this outer layer passes around the pycnidium toward the top, 

 these cells increase in number, become larger, thicker- walled, 

 dark brown in color, and more readily perceptible. At the base 

 of mature pycnidia, this outer portion of the wall is very thin, 



usually only 2 or 3 cells thick, but this thickness is increased to 

 several cell layers on the top and in the vicinity of the beak. 

 The inner layer of the pycnidial wall is composed of irregularly 

 disposed, dilute brown cells, from the innermost row of which 

 the hyaline conidiophores arise. 



Pycnidia range in size upon pods and stems from 82 to 225 \i 

 X 82 to 375 [x, averaging for 131 measurements 169 X 228 [x. 

 On leaf tissues they are somewhat smaller, ranging from 120 to 

 180 x 135 to 240 [l. On stems and petioles the pycnidia are 

 often found to be arranged in rows up and down the stem, and 

 the dimensions of individual pycnidia are as a rule greatest 



