[Vol. 10 



128 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



6. Certain strains of the soybean fungus form perithecia in 

 culture on a variety of media, while no perithecia have ever been 

 found on diseased material from the field. On the contrary, 

 Harter found perithecia on material wintered out of doors but 

 was unable to induce perithecial formation in cultures of the 

 strain derived from ascospores from these perithecia. 



For the greater portion of the time during which pod and stem 

 blight of soybean has been under observation only the imperfect 

 stage of the causal organism was known. The pycnidial sporo- 

 carps agree very well in point of structure with the description of 

 Phomopsis Sacc. as given by Diedicke (11), except that pycnidia 

 of the soybean fungus are more definitely delimited from the 

 host tissue than is indicated by Diedicke's description and draw- 

 ings. In citing the differences between the genera Plenodomus 

 and Phomopsis, he characterizes the pycnidia of the latter as 

 being indistinctly delimited below on account of the hyphal 

 strands pressing between the cells of the host tissue. These are 

 very little in evidence in the case of the pycnidia of the soybean 

 fungus, which in this respect is more like Plenodomus. However, 

 the soybean organism is easily separable from the last-named 

 genus by its long slender conidiophores and the distribution of 

 brown color throughout the pycnidial wall. It differs from the 

 form genus Phoma, to which it was at first tentatively referred, 

 by reason of the thickened stromatic character of the pycnidial 

 wall. The appearance of perithecia in cultures isolated from 

 diseased pods and the demonstration of the pathogenicity and 

 genetical unity of the two stages render the question of the proper 

 position of the pycnidial stage among the imperfect form genera 

 only passing importance. On the basis of the morphology 



of 



of the perithecia the soybean fungus may properly be placed 

 in the ascomycetous genus Diaporthe Nitschke, and since it is 

 parasitic on Soja max (L.) Piper it is assigned the name Diaporthe 

 Sojae. A brief technical description is appended. 



Diaporthe Sojae, n. sp. 



Pycnidia lenticular, subglobose, often flattened beneath, sub- 

 epidermal or immersed in the cortex, simple or sometimes 

 chambered, osteolate, black, 82-225 X 82-375 ;x; beak very 



