504 Journal of Agricultural Research voi. xix. No. 10 



on black raspberry at Rouses Point, N. Y. Collections of the short- 

 cycled rust were made on wild dewberry and wild blackberry at French 

 Creek, W. Va., on wild dewberry at Mountain Lake, Va., and on wild 

 blackberry and dewberry plants at many other points. 



The material collected in 191 7 and 191 8 was brought together for 

 comparison at the end of each season and before there was serious fading 

 in the color of the spores. This comparison has shown that for the 

 material at hand the two orange-rusts exhibit the same color differences 

 regardless of the hosts on which they occur or the localities from which 

 they are collected. The color difference makes it possible to identify 

 the two rusts in the field without resort to spore germination. 



Plate D illustrates the difference in the color of the spores in mass. 



Figure i shows an infected black raspberry leaf, figure 2 an infected 



blackberry leaf. 



MORPHOLOGY OF AECIOSPORES 



In a former paper the writer (7) has pointed out that no morphological 

 differences could be observed between the aeciospores of certain speci- 

 mens of the two orange-rusts. While this statement was true for the 

 specimens under study, it does not hold when larger numbers of speci- 

 mens of the two rusts are compared. A study of more than 100 different 

 collections has shown that the spores of the two rusts differ considerably 

 from each other both in size and in shape. While a few specimens may 

 not reveal this fact, a more extended study shows that the aeciospores 

 of the two rusts are, on the whole, morphologically different. 



In order to show this difference more clearly than is possible by 

 description, an outline drawing has been made of a few typical aecio- 

 spores from a number of different specimens of the two rusts. The 

 drawings were made with the aid of a camera lucida. The same magni- 

 fication was used for all spores, so that the different drawings may be 

 readily compared. There is always a certain amount of variation in 

 the size and shape of the spores of a given specimen. This is greater for 

 some specimens than for others, and it was not always easy to select 

 spores that would be typical. Before material for drawing was chosen, 

 spores from several mature caeomas on each specimen were transferred 

 to separate drops of water on glass slides. They were then observed 

 under the microscope, and a group was finally chosen that seemed to 

 be typical for the specimen in question. Table I gives information 

 regarding the place and time of collection, host, manner of germination, 

 and color of spores in mass for most of the specimens collected in 19 17 

 and 191 8. Numbers given in the last column of the table indicate the 

 drawings in Plates 93 and 94, which show an average sample of spores 

 for each specimen. 



