562 RESEARCHES ON FUNGI 



but, owing to their larger size, they fall in still air somewhat faster 

 than basidiospores, and are transported by the wind proportionately 



shorter distances. 



In Coleosporium the uredospores are produced in basipetal 

 chains below an epidermis the top of which finally breaks open in 

 an irregular manner and is reminiscent of a peridium. It seemed 

 of interest to determine whether or not these spores, whose mode 

 of origin superficially resembles that of aecidospores, are shot out 

 from their sori like aecidiospores. I therefore examined Coleo- 

 sporium Tussilaginis and C. Petasitis from this point of view, 

 placing pieces of the leaves bearing the uredospore-sori in a com- 

 pressor cell in the manner already described for aecidia in the 

 previous Section. It soon became apparent that the uredospores 

 were not being shot away at all but were lying as a loose powder 

 within the peridium. There can be no doubt that the dispersal 

 of these uredospores, hke that of uredospores in general, is effected 

 merely' by the wind which carries them away from their place of 



origin. 



An interesting example of the dispersal of aecidiospores is shown 

 in the accompanying photograph reproduced in Fig. 227. In the 

 centre is a young White Pine, Pinus Strobns, bearing numerous 

 aecidia of the White Pine Blister Rust, Cronartiuin ribicola. These, 

 known as Peridermium Strobi, were full of powdery aecidiospores. 

 The tree was struck smartly with a stick, and immediately there- 

 after Dr. Giissow photographed the escaping spore-cloud which is to 

 be seen on the left side of the tree being carried off by the wmd.i 



During high winds, gales, cyclones, etc., enormous numbers of 

 spores of many species are carried up into the air often, doubtless, 

 to considerable heights. It is easily conceivable that spores which 

 have been raised in this way should be borne horizontally for scores 

 or hundreds of miles before they settle. I am inclined to think 

 that long-distance transportation of this kind accounts for the 

 almost simultaneous infection of vast tracts of wheat m we^^tern 

 Canada by Puccinia graminis. It may be that countless millions 



1 Whether or not the aecidiospores contained in the kind of peridium known as 

 periJ^Z, such as that of Cro.^artiu.n ribicola, are violently ^i-harged^^^^^^^ 

 oi a typical aecidium, such as that of Puccinia grarmms, is at present unkno^^n. 



