THE FUNGI 



177 



Autcecious forms, in which the different kinds of spores are produced 

 upon the same plant, and the Hetercecious forms, in which the aeci- 

 dium is produced upon another host, as in the Wheat-rusts and 

 the Cedar-rusts. 



Of the former type a common species in the Eastern United States is Uromyces 

 caladii (Fig. 142), which often appears in great numbers upon the leaves and 

 stems of the Indian Turnip (Ariscema triphyllum} as well as upon some other 

 Araceae. The diseased plants have the leaves much reduced in size, and thickly 

 covered with the small yellowish pustules caused by the aecidia, or first form of 

 spores produced by the Fungus. A careful examination of the upper surface 

 of the infected leaves will also show minute blackish specks, the spermogonia. 

 A section of the leaf shows the crowded mycelial threads occupying the inter- 

 cellular spaces, which become densely interwoven and compacted where the 

 young spore-groups are to form. The young secidium is a globular mass of 

 hyphse, within which a close- 

 set layer of basidia is devel- 

 oped, from whose ends chains 

 of conidia (JEcidiospores) are 

 cut off. These have colorless 

 walls and orange-red, oily 

 contents, and from mutual 

 pressure appear polygonal in 

 section. The outer row of 

 basidia develop similar chains 

 of cells, which become thick- 

 walled, and are coherent so 

 that they form a distinct 

 receptacle which encloses the 

 secidiospores, the whole struc- 

 ture constituting the JEcidium, 

 or secidium fruit. This breaks 

 through the epidermis of the 

 leaf, and the secidium opens, 

 so that it becomes cup-shaped, 

 and as the pressure on the 

 spores is relieved, they become 

 rounded in shape and drop off. 



Teleutospores. If the 

 same plants are examined a 

 few weeks later, there will be 

 found similar pustules, which 



appear black, and on exami- Fm 143 _^ Puc cinia malvacearum, upon Mava 

 nation are found to be com- borealis. B, P. aurea. Section of leaf of Podo- 

 posed of single, thick- walled phyllum, with sorus of teleutospores (X about 



75) . C, a single teleutospore ( X 400) . D, uredo- 

 spore of P. graminis. (After SACHS.) 



spores, borne upon long stalks. 

 These are the Teleutospores, 

 and in this species germinate 

 only after a long period of rest (probably not until the next spring). 



In California an extremely common Rust is Puccinia malvacearum 

 (Fig. 143), which is especially abundant upon Malva borealis, but 

 also causes much damage to the Hollyhock in gardens. Teleuto- 



