THE FUNGI WHICH CAUSE PLANT DISEASE 125 



these prized as table delicacies, and the Laboulbeniales, an order 

 rich in species which are all parasitic upon insects. 



Protodiscales (p. 123) 



The 4-8 to many-spored asci form a flat palisade-like hymenium 

 which arises directly from the mycelium; paraphyses none; spores, 

 one-celled, elliptical or round. 



Key to Families of Protodiscales 



Parasitic 1. Exoascaceas, p. 125. 



Saprophytic 2. Ascocorticiaces. 



Of these families the second contains only one genus and two 

 species found in bark. The first family is aggressively parasitic. 



— , g.lO 292. 327 



Exoascacese 



This is the most simple of the parasitic Ascomycetes, definitely 

 recognizable as such, and is comparable with the Exobasidiales 

 among the Basidiomycetes. All the 

 species are parasitic and many of 

 them very injurious. The mycelium, 

 which can be distinguished from 

 that of other fungi by its cells of 

 very irregular size and shape, wan- 

 ders between the host cells (intra- 

 cellular in one species), or is some- 

 times limited to the region just f,(j. 85.— Exoascus showing myce- 

 below the cuticle. The asci develop Hum and asci. After Atkinson. 



in a palisade form on a mycelial network under the epidermis, or 

 the cuticle, or on the ends of hyphse arising from below the epi- 

 dermal cells. They are exposed by the rupture of the cuticle or 

 epidermis and contain four to eight hyaline, oval, one-celled 

 spores. These by budding, while still in the ascus, may pro- 

 duce numerous secondary spores, conidia, which give the im- 

 pression of a many-spored ascus. The ascospores also bud freely 

 in nutritive solutions. The primary-ascus-nucleus arises from 



