FUNGI. 81 



They are very thick-walled, the walls being dark-colored, so that in mass 

 they appear black, and constitute the "black- rust" stage (Fig. 47, J). 

 Associated with these, but formed earlier, and germinating immediately, 

 are often to be found large single-celled spores, borne on long stalks. 

 They are usually oval in form, rather thin-walled, but the outer surface 

 sometimes provided with little points. The contents are reddish, so that 

 in mass they appear of the color of iron rust, and cause the " red rust " of 

 wheat and other plants, upon which they are growing. 



The classification of the rusts is based mainly upon the size 

 and shape of the teleuto spores where they are known, as the 

 cluster-cup and red-rust stages are pretty much the same in 

 all. Of the commoner genera Melampsora and Uromyces (Fig. 

 47, L i), have unicellular teleuto spores ; Puccinia (n) and 

 Gymnosporangium, two-celled spores ; Triphragmium, three- 

 celled; and Phragmidium (in), four or more. 



The rusts are so abundant that a little search can scarcely 

 fail to find some or all of the stages. The cluster-cup stages 

 are best examined fresh, or from alcoholic material ; the teleuto 

 spores may be dried without affecting them. 



Probably the best-known member of the group is the wheat 

 rust (Puccinia gmminis), which causes so much damage to 

 wheat and sometimes to other grains. The red-rust stage may 

 be found in early summer ; the black-rust spores in the stubble 

 and dead leaves in the autumn or spring, forming black lines 

 rupturing the epidermis. 



Probably to be associated with the lower Basidiomycetes are 

 the large fungi of which Tremella (Fig. 51, A) is an example. 

 They are jelly-like forms, horny and somewhat brittle when 

 dry, but becoming soft when moistened. They are common, 

 growing on dead twigs, logs, etc., and are usually brown or 

 orange-yellow in color. 



Of the higher Basidiomycetes, the toadstools, mushrooms, 

 etc., are the highest, and any common form will serve for study. 

 One of the most accessible and easily studied forms is Coprinus, 

 of which there are several species growing on the excrement of 

 various herbivorous animals. They not infrequently appear on 



