306 Agricultural Experiment Station, Ithaca, N. Y.. 



probably present a paler green color than the perfectly healthy ones,, 

 especially near the surface of the ground. If such plants are care- 

 fully 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 tlie 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 hyj)hae, as they are called, of the 

 fungus, and collectively make up the myceliuin. The hyphae are 

 branched in quite a profuse manner, the successive branches usually 

 forming somewhat more slender hyphae than the parent ones, so 

 that the main hyphae is frequently larger than the branches. 



The hyphae course between and through the cells. Where a 

 bypha 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 

 older portion, and has the advantage of requiring a much less 

 expenditure of energy than if the opening were made of the same 

 size as the hypha. After passing through the cell wall the hypha 

 enlarges to the normal size. 



While the mycelium is comparatively young the inner portion of 

 the hypha is continuous, i. e., there are no cross walls partitioning 

 the tubes into sections. This is a characteristic possessed by a very 

 large group of fungi to which the Artotrogus belongs, known as the 

 PhyGomycetes. The protoplasm within the hypha is finely granular 

 when the mycehum is young, but in the larger threads as they 

 become older the granules become coarser, their contents are not so 

 homogeneous, and the granules tend to collect into groups or very 

 irregular masses, somewliat resembling the protoplasm in some 

 mucors. 



