TWENTIETH ANNUAL MEETING. 



89 



THE RUSTS {Uredinece), FIG. 5. 



Perhaps no group of fungi are so little understood as the one to which 

 our common wheat and oat rusts belong. Although the real nature of the 

 disease was pointed out by Sir Joseph Banks, nearly one hundred years 



ago, a majority of the 

 farmers account for its 

 appearance in their 

 field by attributing it 

 to the rupture of the 

 cells, or the punctures 

 of insects allowing the 

 sap to exude and, evap- 

 opating, leave a yellow 

 deposit. If we examine 

 wheat rust under a 

 microscope, when it first 

 appears, we shall find 

 great numbers of ellip- 

 tical spores of a yellow- 

 ish color, covered with 

 minute spines. These 

 are supported on short 

 stalks and have burst 

 through the epidermis 

 of the leaf. On becom- 

 ing detached they will 

 quickly germinate if 

 they happen to fall in a 

 droj) of water, and if on 

 a wheat plant will pene- 

 trate the ei^idermis and 

 soon develop other 

 spores. These yellow 

 threeTummOT sporcs are the uredo or 

 summer spores of the 

 rust. (Fig. 5, 3.) 

 If the same wheat 



the rust spot will be seen to 



Fig. 5. Puccinia gramines. Wheat Rust. 



1, Section of barberry leaf, showing the ascidiam fruits below and 

 spermagonia above ; 2, unopeu'ed ascidium fruit ; 3, 

 (uredo) spores and one teleutospores; 4, germinating uredospore; 5, 

 cluster of winter (teleuto)8pore8; 6, germinating telentospore, with 

 sporidia forming at the end of the promycelium; 7, sporidia formed; 

 8, sporidia germinating on the under side of a barberry leaf and pene- 

 trating the epidermis. — After De Bary. 



leaf be examined during the fall, 



have become brown or black. The microscope will show the color 

 to be owing to the presence of spores utterly unlike the yellow summer 

 spores. They are dark colored, two-celled, and have a thick, smooth cell 

 wall; and, as their function is to carry the fungus over winter, they are 

 known as winter or teleuto spores. (Fig. 5,V'-) In the spring, if 

 placed in moisture, these throw out slender threads, at the ends of which 

 button-like protuberances are formed, known as sporidia. (Fig. 5,V-) 

 Under proper conditions these will develop into a new fungus, but, strange 

 though it seems, they will not develop on the leaves of wheat plants, 

 although they propagate readily on the leaves of the barberry. Let us 

 follow it and see what comes of it. The upper side of the barberry leaf 

 soon becomes yellow, and if the spot on the opposite side is examined 

 there will be found a beautiful, cup-like cavity filled with thousands of 

 minute golden spheres, arranged in chains (Fig. 5,'), known as ascidi- 



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