170 



BOTANY 



branches, small papillae (sterigmata) grow, from each of which is developed 

 a chain of small conidia, very much as in Albugo. 



Sex-organs. In both Aspergillus and Penicillium the sexual organs (Fig. 

 135, C) consist of two nearly similar short filaments, which become closely inter- 

 twined, and presumably the contents of one pass into the other. About them 

 there is then formed a mass of sterile hyphse, which completely encloses them 

 and forms the wall of the Perithecium, as the closed fruit is called. From the 

 oogonial body the ascogenous hyphse are developed, and the small oval asci 

 (Fig. 135, E) are formed in large numbers. The outer cells of the perithecium 

 form a yellow rind. 



A g 



Fro. 136. Sphserotheca castagnei. A, conidiophore. B, sexual organs. C, young 

 perithecium, optical section. D, mature perithecium. E, single ascus. F, fertili- 

 zation ; the nucleus of the antheridium has passed into the oogonium. G, asco- 

 genous filament developed from the fertilized oogonium. (F, G, after HARPER.) 



Order VII. Pyrenomycetes 



The Pyrenomycetes, or Black Fungi, comprise over ten thousand 

 species, and include a great variety of both parasitic and saprophytic 

 forms. The mycelium may be composed of delicate, quite distinct 

 hyphae, as in the common powdery Mildews, or the vegetative body 

 of the Fungus may be composed of closely coherent hyphee, which 

 in sections apparently form a parenchymatous tissue. Often this 

 cohesion is so great, and is combined with such a thickening and 

 blackening of the cell-walls, that the cell-structure becomes very 

 obscure, and a large, hard, black mass (Stroma) is produced, from 

 which later the fruiting bodies arise. 



Reproduction. The Pyrenomycetes are many of them character- 

 ized by a marked polymorphy ; i.e. spores of several kinds are 



