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 ^cid- 

 ium (pi., uEcidia) was 

 given. This term is 

 now applied to the 

 cluster cups, and those 

 fungi which at any 

 period of their life his- 

 tory produce them are 

 called secidium fungi. 



363. Spermogonia. 

 — On the upper sur- 

 face of the leaves that 

 bear the secidia, notice 

 some small black dots 

 hardly larger than pin 

 points, but which, 

 when sufficiently mag- 

 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 ? 



Fig. 455. — Section through a barberry leaf, 

 showing on the upper side two spermogonia, s,s ; 

 and on the under side, an secidium, a. 



