THE RUSTS OF NOVA SCOTIA. FRASER. 837 



basidiurn bearing a single spore. A few botanists regard the 

 teliospore as an ascus in which the spore- wall is united with 

 the ascus-wall, thus the rusts would belong to the class 

 Ascomycetes. 



The order Uredinales (Uredinae Tul.) to which the rusts 

 belong is divided by Dietel into four families : Melampsoraceae, 

 Coleosporiaceae, Cronartiaceae and Pucciniaceae. The separa- 

 tion is based on the character of the telia and the teliospores. 



In the Melampsoraceae the teiit>sfK)res stand side by side 

 forming one-layered, flattened masses, which are separated with 

 difficulty; or they may be scattered in the tissues of the host, 

 then they are usually two- or four-celled; the genue 

 Uredinopsis belongs to the latter group. The teliospores are 

 always sessile. 



In the Coleosporiaceae the teliospores are united into 

 one- or two-layered, light-coloured, waxy crusts. They germin- 

 ate without a promycelium, the spore cell soon divides 1 into four 

 basidia and each of these produces a large basidiospore about 

 20/x long. The teliospores are sessile except in a South 

 American genus Chrysopsora. 



The Cronartiaceae have sessile teliospores which are formed 

 in series and either separate from each other or remain united 

 in filiform masses, as in Cronartium, or are formed in chains 

 and compacted laterally forming cushion-shaped masses as in 

 Chrysomyxa. 



The Pucciniaceae, which contain the well known rusts r 

 have stalked teliospores either fasicled or free, usually easily 

 vseparable from the host plant, but sometimes, as in the genus 

 Gymnosporangium, embedded in a gelatinous mass. 



Arthur recognizes three families: Coleosporiaccae, Uredin- 

 aceae (the latter including DietePs Melampsoraceae and 

 Cronartiaceae), and Aecidiaceae corresponding to Puccini- 

 aceae. 



The following is a synopsis of the genera represented in 

 north eastern North America. It is largely based on DietePs 

 Uredinales in Die NaturlicJien PflanzenfamiUen. 



