JUNIPER DISEASES 199 



Cause. 



Cedar-apples on juniper are caused by two different species 

 of the rust-fungi, Gymnos-porangium juniperir-virginiancB and 

 G. globosum. The life history of these fungi is described on page 

 192 in the general discussion of several species of the same genus. 

 In the case of the two cedar-apple rusts, the leaves of the juniper 

 are infected by seciospores formed on the apple, pear, haw or 

 other pomaceous host. This takes place diu-ing midsummer or 

 in the fall and no symptoms on the juniper are apparent until 

 late spring of the next season. At that time the infected leaf 

 shows a small greenish outgrowth, and in the summer from this 

 small beginning the large cedar-apple develops (Fig. 32). The 

 tissue inside the gall is made up of a mixture of large host-cells 

 and intercellular mycelium. The outer layers of the gall are 

 corky and reddish or chocolate-brown. Scattered over the sur- 

 face, in late autumn, are numerous depressions from each of 

 which a bundle of hyphse grow out the following spring and 

 form the horns covered with teliospores. 



References 



Hesler, L. R., and Whetzel, H. H. Manual of fruit diseases, pp. 63- 



71, 341-344, figs. 17-19, 94. 1917. 

 Weimer, J. L. Three cedar rust fungi, their life histories and the 



diseases they produce. Cornell tJniv. Agr. Exp. Sta. Bui. 390 : 



507-549, figs. 136-157. 1917. 

 Heald, F. D. The life history of the cedar rust fungus Gymno- 



sporangium Juniperi-virginianiB Schw. Nebraska Agr. Exp. Sta. 



Ann. Rept. 22 : 105-113, pis. 1-13. 1909. 

 Reed, H. S., and CrabiU, C. H. The cedar rust disease of apples caused 



by Gymnosporangium Juniperi-virginiance Schw. Virginia Agr. 



Exp. Sta. Tech. Bui. 9 : -3-106, figs. 1-23. 1915. 

 Giddings, N. J., and Berg, A. Apple rust. West Virginia Agr. Exp. 



Sta. Bui. 154 : 5-73, pis. 1-10. 1915. 

 Coons, G. H. Some investigations of the cedar rust fungus. Nebraska 



Agr. Exp. Sta. Ann. Rept. 25 : 217-246. 1912. 

 Pammel, L. H. The cedar apple fungi and apple rust in Iowa. Iowa 



Agr. Exp. Sta. Bui. 84: 1-36, figs. 1-11. 1905. 



