GYMNOSPORANGIUM CLAVARLEFORME 



51 



the disease does appear, spraying with Bordeaux mixture is the 

 best remedy against its spreading. It is the very young shoots 

 and the upper side of the leaves that most require spraying ; 

 although the pustules appear chiefly on the lower surface of 

 the leaves, there can be little doubt that infection by the 

 basidiospores takes place mainly through the upper surface. 



Gymnosporangium clavariaeforme. 



The Hawthorn and Juniper Rust. 



This fungus produces its secidia on the branches, leaves and 

 fruit of the Hawthorn and on the leaves of the Pear, and its 

 teleutospores (there are no uredospores) on branches of the 

 common Juniper, where it causes fusiform swellings. There 

 are three other allied British species, of which G. Sabinae also 

 attacks the Pear, but its teleutospores are formed only on 

 Juniperus Sabina (the Savin Juniper). 



On the swollen branches of the Juniper, the parasite pro- 

 duces in April and May numerous orange masses, which ooze 

 out and sometimes reach more than 

 1 cm. in height. They vary in 

 shape, but are usually more or less 

 conical or tongue-shaped (Fig. 30). 

 They consist of a mucilaginous 

 mass in which large numbers of 

 teleutospores are embedded. The 

 mucilage is produced by the gela- 

 tinisation of the cell-walls of the 

 fungus, especially of the very long- 

 pedicels ; it naturally swells and 

 becomes more conspicuous in wet 

 weather. The teleutospores ger- 

 minate at once, while still in the 

 mass ; the basidiospores are pro- 

 duced in the usual way ; it has 

 been shown lately in another species 

 (Coons, 1912) that they do not fall off, but are jerked off the 



4—2 



Fig. 30. Gymnosporangium cla- 

 variaeforme. Masses of teleuto- 

 spores on branch of Juniperus 



(■■mi munis (slightly reduced) ; 

 two teleutospores, x GOO. 



