Mycclunu of the Ustilaginece. 59 



stem, espcciall)' in the nodes. The mycelium consists of 

 hyaline tubes, frequently septate, and enclosing watery or 

 pellucid, frequently vacuolated contents (Plate V. Figs, i, 2). 

 Its walls vary in thickness, but very often they have a 

 distinctly double contour. The number and frequency of 

 the septa are subject to much variation ; in some instances 

 they are close together, at others they are only found at 

 distant intervals. This is also the case with the mycelial 

 ramifications ; sometimes the hyphai do not extend for 

 more than 2^ without branching, at others they extend 

 for 20/x or more without dividing. These long unbranched 

 hyphas are found mostly in the internodes ; in the nodes 

 themselves not only are the branches more abundant and 

 convoluted, but here too are encountered, more abundantly 

 than elsewhere, the little intercellular haustoria, or suckers, 

 which characterize the mycelia of many of the Ustilagineae. 

 The mycelium ramifies not only between the cells of the 

 host-plant, but, frequently piercing their walls, grows through 

 them. Its diameter varies from 2 to 5^. The addition 

 of caustic potash to a section of the host-plant containing 

 mycelium renders the latter more distinct, and otherwise 

 clears up the preparation ; so does prolonged treatment in 

 glycerine. Its walls are not composed of cellulose, as 

 they do not show any blue reaction when treated with 

 sulphuric acid and iodine ; but in some cases, as with 

 U. maydis and Sorosporiiun saponartcs, they do get an 

 external coating of cellulose from the tissues of the host- 

 plant, which, completely investing them, hides them from 

 view (Plate VI. Fig. 3). The mycelium of almost all the 

 Ustilagineae permeates more or less the whole of the 

 affected plant, and although in the advanced state we 

 can find it only near the spore-beds, yet originally it could 

 be found in all parts of the axis of the young plant. In 

 this it differs from the localized mycelia of most of the 



