the Physiology of Parasitism . IL 391 
gauge roughly the stage of infection as, soon after penetration of the leaf, 
the tissues in the neighbourhood of the point of entry become brown and 
then black. The blackening is, of course, a well-known enzymic effect. 
In studying later stages of penetration the sections were stained with 
gentian violet and orange G, or iron-alum-haematoxylin and erythrosin, or 
Delafield’s haematoxylin and eosin (Durand, 4 ). In the very earliest stages 
of penetration iron-alum-haematoxylin was used, followed by scharlach 
red (in equal parts of glycerine and water) ; such preparations which were 
mounted in glycerine showed the cuticle stained very sharply. Gentian 
violet in dilute solution was found useful in demonstrating the stratification 
of the swollen subcuticular wall ; the layering was particularly clear in 
preparations mounted in ‘ euparal \ 
To demonstrate the outer mucilaginous layers of the walls of the germ 
tubes and hyphae, fresh material was mounted in ‘ collargol a preparation 
of colloidal silver. The mucilaginous layer then appears as a clear area 
round the ordinary cell-wall. The mucilaginous coating can also be 
demonstrated by staining fresh material in dilute watery gentian violet and 
mounting in water. 
Observations. 
Germination. The dry conidia swell when placed in turnip juice and 
in 3-3 hours show the first signs of a germ tube. In a highly nutrient 
medium like turnip juice growth is very rapid, and in 15 hours the germ 
tube may reach a length of nine spore-diameters. If the germ tubes are 
growing in drops on a glass plate numerous appressoria will usually be 
formed in 24 hours, and at the end of 36 hours numerous cross-connexions 
are to be seen between the hyphae. These connexions and the interweaving 
of the hyphae convert the originally separate growths into a more or less 
felted mass. 
The germinated spores show numerous nuclei ; in the germ tube the 
nuclei are seen to be arranged in pairs (PI. X, Figs. 6, 7, 8), and usually 
show conjugate divisions (Welsford, 12). 
Anchorage of the germ tube. It was noticed early in the investigation 
that young germinated spores, even before any haustoria were developed, 
usually showed no tendency to become detached from the leaf as a result 
of the manipulation entailed in fixing, washing in running water, &c. The 
cause of the strong adhesion of the young germ tubes to the leaf was found 
to be the mucilaginous nature of the outer layers of the wall of the germ 
tube. This appears to have been overlooked by previous workers owing to 
its transparency ; but it is easily demonstrated by mounting the germinating 
spores in a fine suspension of dark coloured particles. This method was 
first employed by Errera ( 5 ) to demonstrate the gelatinous sheath round 
filamentous algae. Instead of the Indian ink used by Errera a preparation 
E e 
