1014 Walter H. Burkholder 



Fusarium martii phaseoli produces these strands, which at times develop 

 into coremium-like structures of fructification. 



The mycelium in the host rarely extends any distance above the surface 

 of the soil. In its growth in the cortex it possibly reaches its greatest 

 height; here, at times, the coloration due to the fungus may appear on 

 the lower part of the stem. The mycelium in the cortex of the upper 

 part of the root does not penetrate into the vascular bundles, hyphae 

 having been observed to enter the vascular system only through the 

 small lateral rootlets on the lower part of the taproot. The mycelium 

 does not long remain intercellular, but soon enters the cells of all the 

 tissue. From the lower part of the taproot the hyphae progress upward 

 through the cells of the vascular system. Frequently they fill these cells 

 or cause them to collapse, but seldom is a wilting of the host plant pro- 

 duced. The growth of the fungus is extremely slow; by harvest time 

 of the host it frequently has not reached within an inch of the surface 

 of the soil. The height that it attains in the vascular tissue, however, 

 depends on the time of infection. 



F. martii phaseoli produces two kinds of spores on and in the bean roots. 

 They are the chlamydospores and the conidia of the fungus. The chlamy- 

 dospores are borne singly, or, less frequently, in small chains within the 

 host tissue. For the most part they are found in the cortex. In the 

 smaller fiber-like rootlets they occur in greater numbers than in the 

 larger lateral roots and in the taproot. This is due probably to an absence 

 of sufficient food material in the smaller roots. Repeated attempts to 

 germinate these spores have failed. Evidently the optimum set of con- 

 ditions governing germination has not been discovered. Conidia are 

 rarely produced in abundance on the host during the growing season. 

 Frequently spores cannot be found even on severely diseased roots. 

 Before the cause of the dry root-rot was determined, many specimens of 

 infected bean roots were examined without success in finding the spores 

 of the causal organism. A few instances only have been observed of 

 large production of conidia on the dead parts of affected roots. Such 

 cases were during rainy weather, and then the production was so great 

 that the roots appeared whitish. Apparently a sufficient number are 

 always produced for the dissemination of the fungus. In many of the 

 infested fields a small quantity of soil will contain the pathogene to such 



