24 



STRUCTURE AND CLASSIFICATION OF FUNGI 



forms they are developed in particular areas and become surrounded 



and protected by a dense mass of tissue, thus forming a special fruit- 

 ing organ (the ascocarp) , This may be arranged as 

 a hollow sphere (the perithecium) or as a cup-like 

 structure (the apothecium). The fruiting bodies of 

 the cup fungi (Fig. 15) are apothecia. Their inner 

 walls are lined by the asci in a continuous layer, the 

 hymenium which appears in section in Fig. 16. 



In addition to the ascospores, many Ascomycetes 

 also multiply by the production of exogenous asexual 

 spores, the conidia. These are formed in great abun- 

 dance when conditions are favorable for rapid multi- 

 plication of the species, whereas ascospores are often 

 formed only sparsely or under exceptional circum- 

 stances. 



Life Cycle of Ergot. The parasite {Claviceps 

 purpurea) producing a disease of grains, especially 

 rye, and grasses known as ergot may be taken as an 

 example to illustrate the life history of a typical 

 Ascomycete. This organism is of some importance 

 in medicine, since it produces in the infected grains a 

 substance which produces contractions of involun- 

 tary muscles. It has produced poisoning both in 



man and domestic animals, producing abortion by 



inducing contractions of the uterus, and gangrene 



by causing constriction of blood vessels. It is also 



used as a drug to produce a firm contraction of 



the uterus after childbirth. 



The fungus grows in the seeds, which, as they 



develop, become much larger than the healthy 



grains. The tissue of the grain is gradually re- 

 placed by mycelium. During this period the 



fungus reproduces by the non-sexual conidia 



(Fig. 17) formed on the surface of the grain. 



These are accompanied by a secretion of "honey- 

 dew" which attracts insects. They carry the 



conidia to the flowers of other plants, which thus 



become infected. As the grain ripens, those seeds 



which are infected are completely replaced by the 



mycelium, which now dries out and forms a 



dense, hard, black mass, the sclerotium. This retains the general 



form of the seed but is larger and projects considerably from the 



Fig. 16. Section 

 through an 

 apothecium of 

 Peziza showing 

 asci. Some are 

 undeveloped. 

 Two contain 

 the full com- 

 plement of 

 eight asco- 

 spores. 



Fig. 17. Formation 

 of conidia by 

 Claviceps pur- 

 purea. Stained 

 section of a grain 

 affected with ergot. 

 Only a portion of 

 the fungus on the 

 surface is shown. 



