Ernest S. Salmon. 
218 
on six leaves of barley and on one leaf of wheat. 1 After 24 hours one 
barley leaf was examined microscopically. 2 A germ-tube, provided 
with an appressorium, had been produced by nearly all the conidia. 
In the greater number of cases a tube penetrating the epidermis 
had been emitted by the appressorium, and had formed an incipient 
haustorium in the host-cell. (PL V.. figs. 3 and 7 i.h.) The incipient 
haustorium, which was often of a smaller size than those represented, 
consisted of a roundish refractive body. The actual point of pene¬ 
tration could be seen very clearly; viewed from above it appeared 
as a minute circular hole at the focus just below the lower wall of 
the appressorium of the germ-tube, where it was closely applied 
to the epidermis. At this stage of development, marked by the 
penetration of the host-cell and the production within it of a small 
refractive body, the incipient haustorium, the growth of the germi¬ 
nating conidium generally ceases. Several conidia, however, were 
observed w T hich had developed a larger, apparently normal, young 
haustorium in the epidermal cells (Fig. 4). 
At the end of 48 hours another barley leaf was examined. 
Here the same formation of the small refractive bodies—the 
incipient haustoria—was observable. It w T as clear, too, that in the 
majority of cases these bodies had ceased growth, and in some cases, 
even by this date, they were beginning to become disorganized. As 
in the first leaf, a few instances were observed here and there in 
which a conidium had produced in an epidermal cell (sometimes 
the subsidiary cell of a stoma) a normal, apparently vigorous 
haustorium, which had now developed at its ends the lobed pro¬ 
cesses characteristic of the present species (Fig. 2). 
On the 3rd day, in the barley leaf examined, the gradual dis¬ 
organization of the incipient or arrested haustorium (still visible as 
a small highly refractive body) was general and could be clearly seen 
in the majority of cases (Fig 7 d.h.) In this leaf again a few of the 
germinating conidia had formed a full-sized, apparently normal, 
lobed haustorium ; in these cases no further growth, as a rule, had 
resulted; in one or two cases, however, a few short, weak hyphae 
had grown out from the appressorium (as e.g. is shown in Fig. 5). 
On the 5th day the two barley leaves examined showed the 
complete arrest of nearly all the incipient haustoria, which were 
1 The barley and wheat leaves were cut off from seedling plants 
and, after inoculation, were kept on damp blotting paper in a 
Petri dish. 
2 A useful and quick method of rendering such leaves sufficiently 
transparent to show the germinating conidia in situ, is to 
immerse them for a few hours in a mixture consisting of two 
parts of alcohol and one part of acetic acid. 
