221 



Dakota, and Wisconsin. 7 Fromme has shown s that the period of viability 

 in the leaf rust of oats, P. coronata, may be as extended as eighty-four days. 

 The spores in this case were stored dry* in a gelatin capsule. Marshall 

 Ward 9 succeeded in securing germination of unrediniospores of P. disperse 

 which had been for sixty-one days in dry air in the diffused light from a 

 north window. Thus, while urediniospores are capable of germinating as 

 soon as mature, they are capable under proper conditions of maintaining 

 their viability for a period of two to three months and probably more. 

 One of these conditions seems to be dryness. Probably the most common 

 limiting factor to long life of urediniospores in nature is a combination of 

 warmth and moisture. In such a case germination probably takes place, 

 thus of course forestalling any long duration of life in the spore. There 

 seems to be no good reason, however, if germination can be avoided, why 

 urediniospores might not survive the winter. That coldness of weather 

 does not destroy ability to germinate is attested by the fact that a number 

 of investigators — Hungerford, 10 , Ward, 11 Carleton, 12 and others — have col- 

 lected viable urediniospores of various grass rusts during the winter 

 months. 



DISTANCE WHICH WIND BLOWN SPORES TRAVEL AND PRODUCE INFECTION. 



It seems to be a fact, although from the nature of the case not fully 

 proved, that urediniospores of the rusts may travel long distances by the 

 wind and produce infection. This, of course, is to be expected of a struc- 

 ture which can stand drying for so long a time and is so light in weight. 

 Klebahn 13 calls attention to a sand storm which arose in northern Africa 

 and progressed northward over Europe, transporting various mineral 

 particles to various places in Europe. He adds that without doubt the rust 

 spores, which are much lighter than the mineral particles, are much easier 

 transported by air currents. Under the circumstances they would remain 

 suspended much longer and could be carried at least as far and perhaps 

 farther than the mineral particles. The same investigator 14 proved the 

 presence of spores in the air high off the ground by constructing traps for 

 the spores and exposing them in trees and on buildings. He was able in 



'Bur. Plant Ind. Bull. 216:52. 1911. 



«Bull. Torrey Club 40:518. 1913. 



'Ann. Mycol. 1:138. 1903. 



1 'Phytopathology 4:337-338. 1914. 



"Ann. Myc. 1:132. 1903. 



'-Div. Veg. Phys. and Path. Bull. 16:44. 1899. 



13 Die wirtswechselnden Rostpilze68. 1904. 



"1. c. 68. 



