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PART IV. — VEGETABLE TAXONOMY. 



graminis, may be taken as an illustration. This first makes its 

 appearance in the form of yellowish or rust-colored patches on 

 the stems and leaves of Wheat and other grasses. These spots 

 are due to multitudes of yellowish spores, called itredospores, 

 produced from a mycelium growing within the plant. These 



Fig. 524. — Puccinia graminis. A, part of thin cross-section of Barberry leaf showing 

 four secidium-fruits, a, a, a, a, in various stages of development on the under surface, and 

 four spermogonia, sp, imbedded in the upper surface. B, group of ripe teleutospores 

 bursting through the epidermis, e, of a leaf of Triticum repens. C, Uredospores, r, and 

 teleutospore, t, more highly magnified. A, slightly magnified; B, magnified about 190 

 diameters, and C, magnified about 390 diameters. After Sachs. 



spores are dispersed by the wind, and if the season is damp and 

 warm the infection rapidly spreads from plant to plant. 



Spore production of this kind continues until toward the close 

 of the growing season, when the rust-like patches change to a 



