THE WHEAT RUST 



6S 



of each basal cell now grows a slender stalk; the end of 

 this stalk is cut off by a wall, swells, and becomes an egg- 

 shaped summer spore (Fig. 28). When the summer spore is 

 ripe, it is easily broken away. 



After the first summer spore has begvin to develop, a second, 

 and sometimes a third and a fourth, each with its stalk, may 

 be formed from the same basal 

 cell. Thus a single sorus, con- 

 taining many basal cells, con- 

 tinues for some time to produce 

 new summer spores. The sum- 

 mer spores seen separately have 

 a yellowish color ; the sorus con- 

 taining a mass of them appears 

 orange, and it is for this reason 

 that the appearance of the sori 

 on the wheat is spoken of as 

 the "red rust." The summer 

 spores, if carried to other wheat 

 plants, may germinate (Fig. 29, 

 A), causing new infections in the 

 same way that the first infection 

 of the wheat was caused by the 

 spring spores. Thus the summer 

 spores carr\- the infection from 

 one wheat plant to another. If 

 the season is favorable to the 

 growth of the rust, the disease 



may spread in the coiu-se of the stimmer from a few plants 

 that were infected by the spring spores throughout a whole 

 field of wheat. 



94. Winter Spores. — As the end of the growing season 

 approaches, the rust produces spores of still another sort. 

 These are borne in the same kind of sori as are the summer 

 spores, and indeed some of the earhest winter spores often 



Fig. 29. — A, a germinated 

 Slimmer spore ; the young plant 

 growing from it may infect a 

 wheat plant. B, a germinated 

 winter spore; the small plant 

 which has grown from it is 

 bearing sporidia. 



