Volume I I Number 3 



The Plant World 



APRIL, 1908 



A SEARCH FOR RUSTS IN COLORADO. 

 By Prof. J. C. Arthur. 



For a number of years cultures of the Uredinales have 

 been carried on by the writer during the spring season, in 

 order somewhat to unravel the mystery of the heteroecious 

 rusts. When nature bursts into leaf as the sun creeps north- 

 ward, the rusts that have lain dormant during the winter 

 start into life along with the anemone and spring beauty, the 

 gooseberry and thornapple. At this time the dormant rusts 

 of the heteroecious sort may be found on one host, and the 

 young growth on the alternate host. To find a tuft of grass 

 covered with spores of the preceding season's crop and in 

 contact with it some tender shoots with bursting ascia, furn- 

 ishes the best of circumstantial evidence of their genetic 

 connection. If some of the wintered spores yet remain un- 

 germinated, taking them to the greenhouse or sheltered 

 garden and sowing on the associated plant brought from 

 an uninfected locality, will demonstrate the soundness of the 

 inference. To trace a burglar by his footprints in the snow, 

 it is best to start early before casual passers-by have obscured 

 the evidence; and to trace the heteroecial transfer to the 

 alternate host, it is best to be in the field early before later 

 infections and stray spores have started rusts on many plants 

 and destroyed the significance of juxtaposition. 



Short trips have been taken each year for gathering 

 material and making observations for the work, and one 

 species after another has yielded up the secret of its life-cycle. 

 Finally, inspired by the fame of Colorado for its abundant 



