JUNIPER DISEASES 193 



and shrubs as alternate hosts. Unless the necessary alternate 

 host is present in close proximity to the juniper or cedar, the 

 rust cannot exist, since the life history of the fungus cannot be 

 completed. Trees and shrubs of the order Rosales, family 

 Pomacese, are the most common alternate hosts of these fungi. 



The life history of all the Gymnosporangium rusts is similar 

 and is described here to avoid repetition below. As stated, these 

 fungi are parasitic throughout their life. They live for a time 

 on a certain species of juniper or cedar and produce spores 

 (basidiospores) which can only cause infection of the leaf, twig 

 or fruit of a certain few or perhaps only a single species of the 

 wild or cultivated apple-like trees, such as apple, pear, quince, 

 haw, mountain ash and service-berry. Here the fungus lives 

 only for a short time and produces spores (seciospores) which 

 do not reinfect other trees of the same kind but can only infect 

 the required juniper or cedar. Thus it is seen that the spores 

 produced on each of the two kinds of hosts are innocuous to the 

 same host and must find lodgment on trees of the other type in 

 order to continue the life history. 



These rust-fungi over-winter as mycelium in the juniper or 

 cedar leaves or stems. The next season after infection occurs, 

 most of these fungi cause some type of over-growth of the tissues. 

 Such abnormalities are brought about as long swellings or glo- 

 bose galls on the stems, witches'^brooms and leaves transformed 

 into brown globose growths known as cedar-apples. A few of 

 the species cause no abnormal growth and are evident oWy by 

 the fruiting-structures. The fungi form spores (teliospores) in 

 the early spring on masses of mycelium pushed out from the bark 

 of the twig or ^epidermis of the leaf. These spore-masses may 

 be in the form of cushions or ridges in the crevices of affected 

 bark or, in the case of the cedar-apples, they consist of long 

 horn-like projections, sometimes an inch or more in length. 

 They appear at first dark brown, due to the color of the telio- 

 spores on the surface. In wet weather the spore-masses become 







