1923] 



LEHMAN — POD AND STEM BLIGHT OF SOYBEAN 113 



weather, resulting in many more plants becoming diseased as 

 they approach maturity. 



On pods. — When infective material is inserted into the wall 

 of the pod, the mycelium spreads in all directions from the 

 point of inoculation, growing throughout the wall tissues of the 

 pod beneath the epidermis. The mycelial advance in the sub- 

 epidermal tissues is marked by changes which give rise to a 

 watery appearance of infected areas. When infection is more 

 general, such as results from atomizing pods with a suspension of 

 pycnospores, the watery appearance does not develop, but the 

 color of the pod changes to a light brown, which is not greatly 

 different from that of undiseased, ripened pods. In the course 

 of about 10 days of favorable conditions, the entire pod wall 

 becomes invaded, and numerous low, black pycnidia push through 

 the epidermis and soon begin exuding pycnospores (pi. 10, fig. 1). 

 Contemporaneously with pycnidial development, the mycelium 

 invades the seed cavity and attacks the developing seed, often 

 surrounding it with a conspicuous white fungous layer (pi. 12, 

 fig. 1) and penetrating the seed-coat (pi. 9, fig. 3). Pure cultures 

 of the parasite may readily be obtained by carefully breaking 

 open such pods and transferring bits of this mycelial layer from 

 the seed to nutrient agar. Invariably, when numerous pycnidia 

 have developed over the surface of the diseased pods, the seeds, 

 which may have attained nearly mature size, are covered with 

 a more or less conspicuous weft of mycelium, are badly shrunken 



and wrinkled, and are incapable of germination. Pods are 

 found renresentine various 



degrees of this diseased condition 



Pods obviously diseased but bearing no surface pycnidia are 

 found with seeds characterized by all degrees of shrinking and 

 wrinkling (pi. 12, fig. 1). Shrunken seeds from such pods almost 

 invariably give pure cultures of the organism causing this disease, 

 and in several instances seeds which were plump and unwrinkled 

 were found to be infected. 



Infrequently, the infection may not involve the entire pod, 

 but apparently ceases to advance after invading a small portion 

 of the wall. In such instances, if pycnidia develop at all, they 

 are, of course, confined to the diseased area and are not scattered 

 in characteristic fashion over the entire pod. When very young 



