432 
4) the cells of the peridia are nearly round ; at 5 oblong. From 3 to 4 
the cellular structure is of a light vandyke brown; at 5 a pale yellow. 
I am aware that the structure of the peridia, as described by me, varies — 
——— 
‘ 
in some respects from that by Greville and others, which shows the im- 
portance of photographing so minute objects. Ihave presented sections 
of these for future use. 6 represents the appearance of the peridia 
as seen by the naked eye; 7 their general arrangement and their group- 
ings on the leaves; 8 three cells, showing the parts of which the peridia 
are. composed when magnified about 125 diameters ; 9 the spores con- 
tained in the bottom of the peridia, magnified 125 diameters; 10 repre- 
sents the openings or meshes; 11a leaf of a variety of OC. oxyacantha. 
On one of its lobes, at A, is represented a cluster of peridia of a 
species of Acidium, heretofore undescribed as a parasite on the hawthorn, 
or it may have been confounded with that on the leaves; 14 represents 
