2Ö0 
W. B. Mercer, 
The pycniclia in young cultures on plum agar are all formed by 
symphyogen growth, though they may be formed around a few cells of a 
liypha which itself divides to a certain extent. In section it is impossible 
to distinguish by what method the initial masses have arisen. 
At first the primordia are solid (Fig. 2, /). An internal cavity, 
frequently of irregular outline, in which the spores are formed, soon 
arises (Fig. 2, 2 — 4 ). 
The cavity is not 
always centrally si¬ 
tuated. As the pyc- 
nidium increases in 
size the cavity en¬ 
larges and becomes 
more regular (Fig. 2, 
5 — 7 ). In a short 
time it is packed with 
spores (Fig. 2, 8 ). 
No differentiation is 
observable among 
the cells of the three 
or four layered wall 
surrounding the ca¬ 
vity. Towards the 
apex a mouth arises ; 
which, at first very 
narrow, gradually 
widens as growth 
proceeds (Fig. 2, 7 
— 9 ). As the pyc- 
nidium approaches 
ripeness the wall be¬ 
comes stretched to 
two or three layers 
of flattened irregular 
cells which gradually 
darken in colour. 
The exact manner 
in which the spores 
arise is not easy to 
see; indeed it is only 
possible in very 
young pycnidia. In 
development the ca¬ 
vity soon becomes so 
packed with spores 
Fig. 2. 1 , 2 and 5 —p: Median longitudinal sections 
through pycnidia on plum agar in various stages of 
development (only a portion of the spores — which com¬ 
pletely fill the cavity — shown in p). — 3 , 4 : Central part 
of very young pycnidia. — 10 : Typical pycnospores. — 
11 : Variations of same. — 12 : Pycnospores stained with 
Safranin. — 13 : Wall of pycnidium on Potato. — Fig. /—p 
_ 510^ . JPjg I0 - 12 __ 608/^ 
that, even in sections 
1 /1 thick, it is impossible to see the exact connection between spore and 
wall, and often difficult to tell whether a particular cell represents spore or 
wall (Fig. 2, <?, 9 ). In the very young stages half formed spores are 
comparatively seldom met with; and the spores often lie with their long 
sides in contact with wall cells (a, b , Fig. 2, 5 , 6 ). These facts for a time 
