156 
BASCOMBE BRITT HIGGINS 
different host species, but they may be divided into two main groups 
according to the shape of the ascocarp and its position in the leaf. 
Since the development varies slightly in the two types, the develop- 
ment on P. avium will be described and the others compared with this 
one. 
On this host the production of normal Cylindrosporium conidia 
(macroconidia) ceases usually early in August, and from this time 
until after the leaves fall minute conidia (microconidia) about one 
tenth the length of the macroconidia are formed in great numbers. 
They are abstricted from the apex of short branched conidiophores 
(fig- 39) which appear to be the same ones on which the macroconidia 
were produced earlier. At least they are on the same stroma and in 
similar positions. 
Almost simultaneous with this change in spore form, the stroma 
begins to develop downward through the mesophyll and palisade 
layers of the leaf. This growth is at first composed of separate but 
profusely branched and rather tightly packed threads; but an outer 
pseudoparenchymatous layer is later differentiated. The host cells 
are often surrounded by this mycelial growth and often, especially 
the lignified cells of the vascular bundles, remain so enclosed until the 
fruit body matures the next spring (figs. 6, 8). Before the formation 
of the pseudoparenchymatous covering, coils of densely staining 
hyphae appear in the stroma. Several of these coils, often six or 
eight, are formed in each stroma. Each coil consists of two or three 
turns in the hypha and is made up of several uninucleate cells. Its 
free end is extended as a trichogyne-like structure, which is also 
several-celled and slightly enlarged at the apex. This swollen tip 
extends above the surface of the stroma and ends just above the layer 
of conidiophores from the apex of which the small conidia (spermatia ?) 
are being abstricted. Soon after leaf-fall the trichogyne-like struc- 
tures disintegrate and very soon disappear entirely. The fate of the 
coiled base of this structure is as yet an open question. The dense 
pseudoparenchymatous covering, which about this time develops 
entirely around the stroma, makes the inner portion extremely difficult 
to fix satisfactorily. In material killed November 7 in Flemming's 
weak osmic acid fixer, the coils show decided signs of degeneration. 
They are stained scarcely at all by Heidenhain's iron alum haematoxy- 
lin, when the surrounding cells are deep black. Also in some of the 
material killed later no sign of the coils can be seen. On the other hand, 
