Mycelium of the Ustilaginee. 59 
stem, especially in the nodes. The mycelium consists of 
hyaline tubes, frequently septate, and enclosing watery or 
pellucid, frequently vacuolated contents (Plate V. Figs. 1, 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 hyphe do not extend for 
more than 24 without branching, at others they extend 
for 20u or more without dividing. These long unbranched 
hyphz 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 Ustilaginez. 
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 5u. 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 Sorosporium saponarig, 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 
Ustilagineze 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 
