

i9i 7] ARTHUR— RUSTS OF RUBUS 513 



5 





if drawings are made or the germinating spores preserved dry 

 between thin sheets of mica, and if a large specimen of the host be 

 pressed for the purpose of specific determination. 



The Rubus hosts of the lists were carefully examined by P. A. 

 Rydberg of the New York Botanical Garden, on January 30, 191 7, 

 and the names used are in accordance with his judgment. Of 

 course, no person can name species of Rubus with much confidence 

 from leaves alone, as in many collections of the rusts, but the list 

 presents the nearest approach to accuracy at present possible. 

 The species have been listed under the divisions of the genus, 

 and with the serial numbers of the species as given by Rydberg in 

 his monograph of the genus Rubus in the North American Flora, 

 better to show the relation of the hosts and their possible suscepti- 

 I bility to the rusts. Whenever the specimen is said to come from 



a cultivated plant, it has been so indicated. 



In only one instance have aecia and telia been found on the 

 same plants. Only from Van Cortlandt Park and a few other 

 places in the vicinity of New York City, and from Glen, New 

 Hampshire, have the germination of the spores been satisfactorily 

 I observed. In all other cases the aecia of the Gymnoconia and the 



caeomoid telia of the Kunkelia have been separated largely upon 

 arbitrary grounds. The geographical factor in connection with 

 known localities for puccinioid telia has been given much weight, 

 while various other collateral items of information have been 

 utilized. In arriving at a conclusion I have had the valuable 

 assistance of Dr. Kunkel, who kindly went over all the material 

 with me. One reason for making this assortment in detail is 

 the hope of enlisting the interest of any botanist who may have the 

 • opportunity of testing the spore germination in moist air from the 

 localities and hosts named, thus aiding in gradually verifying 



and rectifying the list. 



All present evidence goes to show that the long cycle form on 

 Rubus is essentially a northern species, while the short cycle form 

 is essentially southern. Fig. i shows the present view regarding 

 geographical distribution. The chart is based entirely upon the 

 data given in the preceding lists of hosts, the southern limit of the 

 Gymnoconia being in large part that indicated by the collections of 



