Aug. i6. 1920 Further Data on the Orange-Rusts of Ruhus 503 



four or more cells, and usually four of these contain one nucleus each. 

 Each nucleated cell is capable of producing a sporidium. The germ 

 tubes arising from spores borne on raspberry leaves are long and sinuous. 

 By suitable methods of staining they have been shown to contain two 

 nuclei. At an early stage in germination they may be distinguished 

 from promycelia by their smaller diameter and more rapid longitudinal 

 growth. Temperature, within the range tested, has no ejBfect on the 

 manner in which the aeciospores of these two rusts germinate. In the 

 vicinity of Washington, D. C, at Mountain Lake, Va., and at French 

 Creek, W. Va., both rusts occur side by side under the same conditions 

 of temperature and climate. The writer is, therefore, unable to accept 

 the theory that temperature determines whether spores of a given 

 orange-rust specimen will produce germ tubes or promycelia. 



COLOR OF SPORES IN MASS 



The finding of the two orange-rusts growing within a short distance 

 of the laboratories of the Bureau of Plant Industry made it easy for 

 the writer to compare them more carefully than was possible when they 

 had to be brought from dififerent parts of the country. The comparison 

 of the rusts as they occur side by side on their living hosts has brought 

 to light certain dififerences that were not noticed earlier. One of the 

 most important of these is the color of the spores in mass. 



It soon became evident that the spores of the short-cycled rust are 

 lighter in color than those of Gymnoconia. The spore colors of the 

 two rusts were matched on Ridgeway's color chart. According to this 

 chart the spores of the short-cycled rust are cadmium orange, while 

 those of the long-cycled rust are xanthine yellow. These two colors do 

 not differ greatly from each other and stand side by side in the chart. 

 Nevertheless they can be easily distinguished after one has once noted 

 the difference between them. It is surprising that this difference was 

 not seen earlier, especially since account was taken of the color of the 

 spores in mass. It seems that failure in this regard was due to the 

 fact that the color of the spores of both rusts begins to fade within a 

 few weeks after they are collected, and differences in shade of color were 

 attributed to fading. 



It was at first thought that the difference in color between the spores 

 on raspberry and on blackberry leaves might be due to the difference 

 in host. In order to test this hypothesis a number of collections were 

 made during the spring of 1917 and 19 18. The long-cycled rust was 

 collected on both wild and cultivated black raspberry at French Creek, 

 W. Va. It was collected on wild blackberry (identified as Ruhus 

 alleghaniensis) at Mountain Lake, Va. Numerous collections were 

 made in the Adirondack Mountains near Old Forge, N. Y., and in the 

 White Mountains near Glen and Jackson, N. H. It was also collected 



