340 Boyle . — Studies in the Physiology of Parasitism. VI. 
the cuticle very deeply, so that the early stages of penetration can be 
observed. Sections were also stained by Durand’s method (7). 
Observations. 
The mycelium of the fungus grows vigorously in dilute turnip juice 
prepared as described above. The hyphae are colourless, rather closely 
septate, and much branched. In hanging-drop cultures numerous cross-con- 
nexions are established after 24 hours, and in a few days a dense white weft 
of mycelium is formed. At a later stage the fungus produces numerous 
structures resembling conidia in grape-like clusters on conidiophores after 
the manner in which conidia are borne by Botrytis , but these structures, 
whatever their true nature may be, have not so far been induced to 
germinate. 
In hanging-drop cultures of turnip extract the hyphae are enveloped 
in a thick mucilaginous sheath, which can be easily demonstrated by 
mounting a piece of actively growing mycelium in Indian ink, as was 
employed by Errera (8) to demonstrate the gelatinous sheath round the 
filamentous algae. In such preparations the sheath appears as a clear halo 
round the hyphae against a black background (PI. XIV, Fig. 1 ). After standing 
for a few minutes the particles of ink became aggregated along the margin of 
the sheath, giving it a much darker appearance than the general background. 
The presence of the sheath can also be demonstrated by staining with dilute 
aqueous gentian violet for 30 seconds and mounting in water. It is broadest 
round .the main branches of the hyphae (Fig. d) and gradually becomes 
narrower towards the growing tips (Fig. 1). By means of this mucilaginous 
sheath the mycelium adheres to the surface of the host and consequently 
shows little or no tendency to become washed off in the fixing and 
subsequent operations. In fixed and stained preparations it can no longer 
be observed as such, but its remains are sometimes visible as fine threads 
which connect the hyphae to the substratum (Fig. 6). 
When the tips of actively growing hyphae in a hanging-drop preparation 
come into contact with the glass they form short branches on which arise 
tufts of secondary branches, and thus large appressoria are formed, by means 
of which the mycelium adheres firmly to the cover-slip. These also are 
surrounded by a mucilaginous sheath which shows up very distinctly when 
mounted in Indian ink (Fig. 5). 
In four-day-old hanging-drop cultures of the fungus in turnip juice 
many of the appressoria are observed to show very distinct hyaline 
circular areas on the surface of the appressorial branches in contact with the 
glass — giving the impression of pores (Fig. 4). One or several such areas 
may be developed on each branch. From these, small infection hyphae 
are sent out, which, in nutrient media, grow into normal vegetative hyphae 
(Figs. 4 a, 4 by 4 c). In young appressoria these differentiated areas are not to 
