10 H. E. Thomas and W. D. Mills 



On foliage 



Only the apple and hawthorn rusts have been found on apple foliage. 

 On the upper (ventral) leaf-surface the spots are strikingly similar in 

 appearance. However, on the varieties and seedling trees that have 

 been studied, the hawthorn rust produces, on the average, distinctly 

 smaller lesions (Plate I, 1), and none has been seen which equals in size 

 those produced by the apple rust on a variety such as Wealthy. It is 

 interesting to note that Wealthy foliage is highly resistant to hawthorn 

 rust in inoculation experiments, the lesions produced being at most about 

 1 millimeter in diameter. On the lower (dorsal) leaf-surface, several 

 distinguishing characters may be found. With the hawthorn rust the 

 accia are relatively few in number and are closely aggregate in the cen- 

 ter of the lesion, and the adjacent leaf tissue in the lesion is of a light 

 orange color. The peridial tubes are persistent and long, sometimes 

 reaching 3 to 5 millimeters in length (Plate I, 2). These dehisce irreg- 

 ularly, never becoming markedly revolute. 



In contrast, the apple-rust spots bear numerous aecia scattered over 

 the lesion, sometimes forming a ring near the margin of the lesion, and 

 the peridia are strongly revolute, especially when moist (Plate I, 6). 



The two diseases can be readily distinguished by examining the ter- 

 minal cells of the peridia mounted in water (Plate I, 3, 4). The dif- 

 ferences are by no means so striking if cells are taken from near the base 

 of the peridial tube. The terminal cells of G. juniperi-virginianae are 

 relatively long and narrow, separate readily in water, and are strongly 

 curved. The comparable cells of G. globosum are irregularly lanceolate 

 in face view, and adhere in a pseudoparenchymatous plate when mounted 

 in water, curving slightly or not at all. 



On fruit 



The usual symptoms produced by apple rust on apple fruit are well 

 known. Gardner (1925) has figured and described symptoms on Rome 

 and Gideon fruits, however, which are strikingly different from those 

 commonly encountered. 



The quince rust on apple fruits presents a wide range of symptoms 

 which on different varieties may be almost completely dissimilar, vary- 

 ing from hyperplastic to necrotic but in the main hypoplastic or necrotic 

 (Plate II). There is less tendency here for the lesions to be restricted 

 to the calyx end of the fruit, and often several separate infections are 

 found on a single fruit (Plate II, 11). The surface of the lesion is 

 usually of a dark green color, seldom if ever becoming orange on the 

 varieties that we have studied. 



The hyperplastic and hypoplastic lesions produced by the quince 

 rust usually involve considerable areas of the fruit and may be accom- 

 panied in later stages by marked shriveling of the fruit (Plate II, 8). 



