RUSTS 



PRACTICAL QUESTIONS 



279 



1. Why are mushrooms generally grown in cellars ? (25,384.) 



2. Name any fungi you know of that are good for food or medicine 

 or any other purpose. 



3. Name the most dangerous ones you know of. 



4. Do you find fungi most abundant on young and healthy trees, or 

 on old, decrepit ones ? Account for the difference. (384.) 



5. Do you ever find them growing upon perfectly sound wood any- 

 where? 



6. Is it wise to leave old, unhealthy trees and decaying trunks in a 

 timber lot? 



RUSTS 



MATERIAL. A leaf of wheat affected with red rust. A leaf or a 

 stalk with black rust. Some barberry leaves with yellowish pustules on 

 the under side that look under the lens like clusters of minute white 

 corollas (see Fig. 542). As the spots on barberry occur in spring, the 

 red rust in summer, and the black rust in autumn, the specimens will 

 have to be gathered as they can be found, and preserved for use. 



In the southern States barberry occurs but rarely or not at all, and a 

 different species of rust, the orange leaf (Pucctnia rubigo-vera), is more 

 common than the ordinary wheat rust {Puccinia graminis), but the two 

 are so much alike that the directions given will do for either. If the 

 orange leaf rust is used, the cups and pustules should be looked for on 

 plants of the borrage family comfrey, hound' s-tongue, etc. Leaves 

 of oats or other infected grasses may be used, but wheat is to be pre- 

 ferred, as the life history of the common wheat rust (/*. Graminis) 

 has been more clearly traced than that of any other variety. The apple 

 scab fungus may be used instead of wheat if more convenient. In this 

 case, provide apple or haw leaves affected with scab, and some of the 

 common excrescences known as cedar apples. 



399. Red Rust. Uredo Stage. Examine a leaf of " red 

 rusted " wheat under the lens, and notice the little oblong 

 brown dots that cover it. These are the sori, or clusters 

 of sporangia that have formed upon the surface. Viewed 

 under the microscope the red rust is seen to consist of 

 a mycelium that ramifies through the tissues of the leaf 

 and bears clusters of single-celled reddish spores that 

 break through the epidermis and form the reddish brown 

 spots and streaks from which the disease takes its name. 

 These spores, falling upon other leaves, germinate in a few 



