320 PRACTICAL COURSE IN BOTANY 
microscope and notice that the yellow substance is com- 
posed of regular layers of colored spores. The corolla-like 
receptacles containing them, popularly known as “ clus- 
ter cups,” are borne on a mycelium produced from the 
spores described in the last paragraph. This mycelium is 
parasitic on barberry or other leaves, according to the kind 
of fungus, and was long believed to be a distinct plant, to 
which the name Acid- 
tum (pl., Aicidia) was 
given. This term is 
: now applied to the 
4... Cluster cups, and those 
ay fungi which at any 
yD. period of their life his- 
ay ~, tory produce them are 
ee et 6 called ecidium fungi. 
363. Spermogonia. 
—On the upper sur- 
face of the leaves that 
bear the ecidia, notice 
some small black dots 
hardly larger than pin 
Fie. 455.—Section through u barberry leaf, points, but which, 
showing on the upper side two spermogonia, s,s; when sufficiently mag- 
and on the under side, an ecidium, @. nified, appear as little 
flask-shaped bodies (Fig. 455) under the epidermis. These are 
known as spermogonia, or pycnidia. When mature, they 
break through the epidermis so that the necks protrude, and 
discharge a quantity of minute cells or spores, very like some 
that, later on, we shall find playing an important part in the 
reproductive processes of certain other fungi, and of mosses 
and liverworts. In the rust fungi, however, their function is 
not understood. They may possibly be survivals of organs 
which were once active in the life processes of the plant, but 
have become useless under changed conditions. Do such 
organs throw any light on the evolutionary history of plants? 
