552 



RESEARCHES ON FUNGI 



in the 12 individual pustules being as follows : 178, 130, 127, 97, 74, 

 48, 28, 15, 11, 9, 8, and 7. Reckoning 11,000 aecidiospores to each 

 aecidium, the total number of aecidiospores produced by the leaf 



was 8,000,000. 



From the above calculation 

 it appears that a leaf of Berberis 

 vulgaris well infected with 

 Puccinia graminis produces from 

 about 4,000,000 to 8,000,000 

 aecidiospores. A Barberry bush 

 with 200 leaves, each leaf pro- 

 ducing on the average 5,000,000 

 aecidiospores, would produce a 

 total of 1,000,000,000 spores. 

 It is probable that the 3,000 

 bushes infected with Puccinia 

 graminis in the spring of 1918 at 

 Winnipeg produced upwards of 

 2,000,000,000,000 aecidiospores. 

 The Violent Discharge of 

 Aecidiospores. — In 1883, Zalew- 

 ski 1 discovered that the aecidio- 

 spores of certain Uredineae, 

 when ripe, are shot out of the 

 aecidia with considerable vio- 

 lence. Since Zalewski's discovery 

 seems to have been entirely over- 

 looked by modern uredinologists 

 and is nowhere mentioned in 

 botanical text-books, I shall here 

 describe it in detail. 



Zalewski placed some leaves 

 of Euphorbia Cyparissias, which bore aecidia of Uromyces Pisi, on 

 glass slides under a bell-jar containing moist air in such a way that 

 some of the aecidia looked directly upwards. He then suspended 



1 A. Zalewski, " Uber Sporenabschniirung und Sporenabfallen bei den Pilzen," 

 Flora, Jahrg. LXVI, 1883, pp. 268-270. 



Fig. 226. — Four pustules of aecidia of 

 Puccinia graminis, the Black Stem 

 Rust Fungus, on the under side of a 

 leaf of Berberis vulgaris, the Common 

 Barberry. Each aecidium produced 

 about 11,000 aecidiospores. Photo- 

 graphed by J. E. Howitt at the 

 Ontario AgriculturalCollege,Guelph. 

 Magnified about three times. 



