236 BULLETIN 94. 



The conditions of the aerial portions of the plant at this early 

 stage of its fall are largely dependent upon the moisture content 

 of the atmosphere. If the moisture be quite dry the seedling will 

 be quite flabby before it falls and will soon wilt thereafter, but if 

 the moisture content is large the tissue will remain quite firm for 

 a time unless the soil upon which it is lying is so saturated with 

 moisture as to encourage the rapid growth of the fungus in the 

 prostrate portion of the plant. When this is the case the entire 

 plant soon becomes a putrid mass and the tissues often take on a 

 dark color. 



After attention has been called to the trouble by the preliminary 

 collapse of a few plants, if others are carefully noted some will 

 probably present a paler green color than the perfectly healthy 

 ones, especially near the surface of the ground. If such plants 

 are carefully examined they will probably show the presence of 

 the fungus in the tissues of the root and lower part of the stem, 

 for the fungus requires several hours after entering the tissues to 

 produce such changes which would be visible to the unaided eye. 



Mycelium. If from one of these prostrate plants a portion of 

 the collapsed part of the stem is teased apart on a glass slip, such 

 as is used in microscopic work, in a little water and then examined 

 under the microscope the vegetative phase of the parasite will prob- 

 ably be apparent. It exists as slender, colorless, thread-like 

 irregular tubes, which appear to be more or less tangled in the 

 tissues of the seedling. These tubes are the hyphae, as they are 

 called, of the fungus, and collectively make up the mycelium. 

 The hyphae are branched in quite a profuse manner, the succes- 

 sive branches usually forming somewhat more slender hyphae than 

 the parent ones, so that the main hypha is frequently larger than 

 the branches. 



The hyphae course between and through the cells. Where a 

 hypha passes through a cell wall it is very much constricted or 

 very much more slender than it is in the cell lumen of the seed- 

 ling or between the cells. The hypha in boring its way through 

 these walls excretes a ferment, it is supposed, which dissolves the 

 cellulose of the walls at the point of contact. A quite minute 

 opening in the wall is sufficient for the growing end of the hypha 

 to squeeze its way through and maintain communication with the 



