Disease of Greengage Trees. 213 
As before mentioned, in the quite dead distal parts the mycelium 
retreats to the cortex to produce there the pycnidia and apothecia. 
A small portion of such a branch, 1 cm. in diameter and 1 cm. long, 
stripped of bark so as to have a narrow cylinder of cortex, was 
placed in a test tube which contained a pad of cotton wool saturated 
with sterilised water at the bottom. The tube was afterwards 
carefully plugged with wool. After some weeks pycnidia appeared 
from the remains of the cortex. One of these pycnidia at the time 
of writing was extruding a thread of conidia (cf. pure cultures). 
VI.— Pure Cultures. 
It was found very difficult to obtain clean cultures of Dermatella 
prunastri in any quantity from the conidia chiefly owing to the fact 
that only a very small percentage of the conidia germinated. In 
order to make sure of obtaining a few conidia which would germinate 
a number of hanging-drop and plate cultures were made. The 
germination and growth into mycelia were observed in a few 
instances; but as these did not exceed more than three in number 
it has been thought advisable not to describe these till such cultures 
have been repeated. Suffice it to say that the conidia germinate 
at their ends by producing germ tubes which soon branch. The 
subsequent mycelia produced were similar to those formed in 
hanging-drop cultures of the ascospores to be presently described. 
Ascospores in a pure state were obtained by placing detached 
apothecia into a drop of agar situated on the bottom plate of a 
damp-chamber slide. The asci discharged their spores upwards 
into the air of the chamber, the spores adhering to the glass cover 
slip forming the roof of the damp-chamber. The ascospores were 
discharged continuously for three days, and on examination it was 
found that many young and ripe asci were still present so that the 
apothecia in all probability take some days to completely discharge 
all their ascospores. 
In the manner described above ascospores in great numbers 
were obtained. Although many of the groups of discharged asco¬ 
spores were eight in number (Fig. 3, C), yet groups from all numbers 
from one to many hundreds were observed. 
No doubt the aggregation of the spores in large numbers was 
determined by the surface energy of the film of moisture present on 
the cover-glass on to which the spores had been shot. From these 
discharged ascospores clean cultures were made, some of which 
were transferred to damp chambers for the purpose of watching the 
germination; others were plated on various media, and still others 
