8o 
West . — On Stigeosporium Marattiacearum and 
When young, the hyphae are hyaline and possess extremely thin delicate 
walls with a very irregular contour (Text-fig. 3 , a ). At this stage, their 
contents consist of a finely granular cytoplasm in which many relatively 
large nuclei are irregularly distributed ; in other words, the mycelium of this 
fungus exhibits the multinucleate condition typical of the Oomycetes (Text- 
fig. 3 , a , b). 
The walls of the hyphae thicken up with age, assume a light-brown 
coloration, and become highly refractive. Meanwhile the cytoplasm becomes 
Text-fig. 2. Mycelium of Stigeosporium Marattiacearum . a, b, and c are drawn to the same 
magnification in order to show remarkable variation in size and form of the hyphae. From a root 
of Angiopteris evecta, Hoffm. n. = nucleus. 
The contents of the host-cell are not shown, x 750. 
vacuolate and tends to disappear, whilst the oldest hyphae are invariably 
empty (Text-fig. 3 , c ). In diameter the hyphae are extraordinarily vari- 
able, ranging from 1 \x in the younger to 13 /x in the older regions (Text- 
fig. 3, a, b, c). 
As stated above, the mycelium within the tissues of the host is both 
inter- and intracellular. In the outer layers of the cortex the hyphae are 
usually intracellular, apparently experiencing no difficulty in penetrating the 
cell-walls of the host (Text-fig. 1). No obvious constriction of the hyphae 
is noticeable at the point where they penetrate the cell-wall, nor does the 
latter develop a tubular sheath around the invading hypha. It is probable 
that the secretion of enzymes, which results in the solution of the cell-wall, 
is confined to the apical region of the hyphae, for, even in very old roots, the 
presence of the fungus never leads to isolation and disorganization of the 
