CHAPTER IX. — THE THALLOPHYTA. 321 



holic fermentation ; and S. Mycoderma, the so-called Flowers 

 of wine. Cells of common yeast and wine-ferment are shown in 

 Fig- 5 2 3- 



CHAPTER IX.— The Thallophyta. 



THE FUNGI (Continued). 

 The ^Ecidiomycetes — The Basidiomycetes. 



The ^Ecidiomycetes, also called the Uredineae, are popularly 

 known as Rusts, and are parasites, forming yellowish, brownish 

 or blackish spots on the stems and leaves of various plants. 

 Some of them, as the Wheat-rust, are highly destructive to crops. 

 The name ^cidiomycetes, refers to a peculiar form of fructifica- 

 tion called " aecidium-fruits," which are. produced by the species. 

 These fruits consist of a cup-shaped envelope or peridium, in the 

 bottom of which rows of cells are formed and separated one 

 after the other, by transverse division, forming rounded spores 

 called cecidiospores. They are only a peculiar form of conidia, 

 and the whole fructifying organ corresponds, doubtless, to the 

 sporocarp of the Ascomycetes. No sexual reproduction has 

 actually been observed in any of the species, yet there is 

 reason to believe it takes place ; for in some, minute sper- 

 matia are formed before the aecidium-fruits develop, and it is 

 probably due to their fertilizing influence that the latter are 

 produced. 



In some species, the aecidiospores, on germinating, produce 

 short, few-celled filaments, constituting a promycelium which 

 soon ceases its vegetative growth and bears small conidia, called 

 sporids or sporidia. These, when deposited by the wind or some 

 other agency on a suitable host-plant, germinate and produce 

 tubes which penetrate the epidermis or enter the stomata and 

 develop a mycelium in the interior of the host-plant, and this 

 mycelium again produces aecidium fruits. 



In some of the species, however, the life-history is more com- 

 plex, there being two distinct stages in it that are spent on differ- 

 ent host-plants, and in which different sets of reproductive spores 

 are developed. Of this group, the common wheat-rust, Puccinia 



