272 HARSHBERGER— A GRASS-KILLING SLIME MOULD. [Novembers, 



to be a fungous disease. It seems that the trouble began eight or 

 ten days before the above date after some showers at night, Httle 

 patches of blackened grass appearing on the lawn in the morning. In 

 a few days, these black patches, if disturbed with the foot or a stick, 

 gave off little clouds of dark brown spores. The original patches 

 were small and few in number, from six to twelve inches in diameter 

 and of irregular shape. The rains and damp weather of early 

 August, 1905, aggravated the injury to the lawn, for the patches 

 spread over much larger areas and covered portions of lawn twenty- 

 five feet in diameter, of irregular outline, with smaller patches scat- 

 tered in the circumscribed space. The disease not only occurred in 

 Cynwyd, but also on some lawns along the main line of the Pennsyl- 

 vania Railroad. Subsequently Mr. Gardner informed me that only 

 the blades of lawn grasses were destroyed, for after the disease had 

 disappeared, leaving the aerial green portions of the grasses dead, 

 the grass over the above mentioned patches regained its fresh, bright 

 green color, proving that the plasmodium of the slime mould had not 

 penetrated to the rootstocks (rhizomes) or to the roots. 



Specimens were sent to me and an examination showed the 

 presence of numerous sporangia of a slime mould, which I deter- 

 mined to be Physarum cinereuni Pers. The blades of grass were 

 killed by the plasmodium of this myxomycete spreading across the 

 surface of the lawn. It is a well-known fact that in damp weather 

 a Plasmodium may grow with considerable rapidity, so as to cover 

 areas of large superficial extent. Such a plasmodium, when active, 

 constantly advances over the substratum by a slow amoeboid move- 

 ment, assuming as it goes a reticulate appearance with numerous 

 pseudopodia extending in many directions out from the margin. As 

 it moves it incorporates many organic substances as food, as I have 

 previously shown,^ and the dejectamenta is left behind in the form 

 of a slimy detritus on the surface of the substratum. The plas- 

 modium of Physarum cinereum Pers. which caused the destruction 

 of the grass blades is a watery, white one found usually among dead 

 leaves in the woods. In the above instance, it left its saprophytic 

 habit, assuming a grass-killing one. The sporangia which are 



^ Harshberger, John W., " Observations upon the Feeding Plasmodia of 

 Fuligo septica," Botanical Gazette, XXXI, 198-203, March, 1901. 



