Amphispores of the grass and sedge rusts* 



Joseph Charles Arthur 



There is but one known exception {Piiccinia graininelld) to the 

 general statement that all plant-rusts occurring on grasses and 

 sedges possess in their life- cycle the full complement of spores 

 characteristic of the Uredineae, L e.^ aecidiospores, uredospores 

 and teleutospores. In the majority of cases knowledge of the 

 cycle is yet incomplete, and the aecidiospores and sometimes the 

 uredospores are yet to be detected and described, but there is no 

 reason to doubt that they exist All grass and sedge rusts belong 

 to either the genus Piiccinia or Uromyces, 



Species of Piiccinia often possess one- celled teleutospores, 

 which are called mesospores. Such spores do not differ struc- 

 turally or physiologically from the normal two-celled teleutospore 

 of the species^ except that the lower cell is wanting. 



A {t\\ species, belonging to both Piiccinia and Uromyces^ 

 possess two sorts of uredospores, which differ both structurally 

 and physiologically, and in the most marked forms the divergence 

 is very wide. A good, and in some ways the best illustration of 

 the two forms of teleutospores and uredospores may be found in 

 Piiccinia vcxans, a species of which Sydow f remarks in his mono- 

 graph of the Uredineae, that here is presented the interesting fact 

 of a Piiccinia with two different teleutospores and two sorts of 

 uredospores. 



Uredospores in general serve the purpose of summer spores 

 for the rapid dissemination oi the species. Their walls do not 

 protect the spore from much drying or great extremes o( temper- 

 ature. As soon as mature they drop away readily, and are free 

 to be blown about by the wind. 



The modified uredospores, to which the name amphispore was 



* Read .before the Indiana Academy of Sciences, at Indianapolis, Nov. 25, 1904. 



Tatsache 



Teleutosporen und zweierlei Uredosporen hervorbringt." Sydow, Monog. Ured. i : 

 736. 1 904. 



35 



