GYMNOSPORANGIUM 317 



ooze through the bark at these swollen points. The gelatinous 

 masses consist of teleutospores which germinate and produce 

 secondary spores without falling away from the tree. These 

 secondary spores are dispersed by wind, and those that happen 

 to alight on the leaves, young shoots, or fruit of the hawthorn, 

 pear, or whitebeam, set up infection which results in the 

 formation of the cluster-cup stage of the fungus. The cluster- 

 cup spores in turn infect juniper branches, but as the mycelium 

 of the fungus is perennial in the juniper plant, after one 

 infection the teleutospores are produced from the same point 

 each season, at the same time the mycelium continues to 

 spread in the branch, and the swelling becomes bigger each 

 year. On the other hand, there is no perennial mycelium in 

 the case of the cluster-cup, hence the hosts require fresh 

 infection each season. 



Aecidia springing in groups from yellow spots, cylindrical, 

 whitish, splitting into recurved shreds, spores in chains, 

 warted, yellowish, 22-45x19-35 /*. Teleutospores oblong- 

 fusoid, yellow, 90-120 X 15-18 //>, pedicel very long. 



As both hosts are absolutely necessary for the continuance 

 of the fungus, the removal of either host stops the disease, 

 which often causes early defoliation and loss of crop. 



Pear leaf cluster-cups (Gymno sporangium sabinae, 

 Winter) produces its teleutospore stage on Juniperus 

 communis, J. oxycedrus^ J. virginiana^ and J. phoenica. 

 The gelatinous masses of spores appear in spring on the 

 branches, as flattened, blackish, then reddish-brown masses 

 about half an inch long. So far as at present known the 

 aecidium only occurs on living pear-leaves, where the horn-like 

 aecidia occur in clusters on yellowish spots. 



Aecidia up to 2 mm. long, mouth closed, spores escaping 

 through lateral slits, aecidiospores in chains, brownish, 

 irregularly globose, delicately warted, 2 2-24 x 17-26 /A. Sper- 

 mogonia present on opposite side of leaf to teleutospores. 

 Teleutospores ellipsoid, chestnut-brown, each cell has 4 germ- 

 pores, 38-50X23-26 /A. 



When pear leaves are badly infected defoliation takes place 

 early in the season, and the crop is seriously affected. 

 Removal of the infected portions of juniper arrests the 

 disease. 



Medlar cluster-cups (Gymnosporangium confusum, Plow- 

 right) closely resembles the pear leaf cluster-cups in appear- 



