438 APPLICATION OF METHODS OF BACTERIOLOGY 



Wright presented the following characteristics: As ob- 

 tained from the affected tissues, the mycelia under the 

 microscope appear as black or brown mulberry-like masses 

 less than one millimeter in diameter. They are hard, rather 

 brittle, and difficult to break up under the cover-glass. On 

 soaking them in a strong solution of sodium hydroxide they 

 become softened and the structure of the fungus-mass can 

 be made out. Under high magnifying power these masses 

 are found to consist of pigment-granules, ovoid translucent 

 bodies, and distinctly branching separate hyphse. Some- 

 times these latter exhibit dilatations or varicosities of their 

 segments. The periphery of a fungous mass shows the pres- 

 ence of club-shaped hyphse, closely set and radially arranged. 

 From such masses growth on artificial culture-media may 

 be obtained. When transferred direct from the tissues to 

 artificial media, growth in every case starts from the granule 

 about four or five days after it is placed upon the culture- 

 media. 



On solid media it first appears as delicate tufts of whitish 

 filaments. These in the course of a few days increase in 

 number and length, and, in the case of the potato, form a 

 dense whitish or pale-brown felt-work having a tendency 

 to spread widely. 



In pure cultivation it is seen as long, branching hyphse 

 with ^delicate transverse septa. In old forms the hyphse 

 may be swollen at the points marked by the septa, and may 

 then appear as strings of plump oval segments. The fila- 

 ments have a definite wall, inclosing granules and pale areas. 

 No spore-bearing organs are seen. 



On potato, it grows as a dense, widely spreading, velvety 

 membrane; pale brown at the centre and white at the 

 periphery. The potato takes on a dark-brown color and 



