INSECTS, DISEASES, AND INJURIES 159 



Several native cedars and junipers and some of their horti- 

 cultural varieties are attacked by a number of fungi belonging 

 to the genus Gymnosporangium. For the completion of the 

 life cycle of these fungi, certain broad-leaved trees and shrubs, 

 such as apple, pear, quince, hawthorn, mountain-ash, juneberry, 

 fire-thorn, are essential, and, upon some of these, serious 

 diseases are also caused by the fungi concerned. One type of 

 spore is produced on the junipers and cedars and another type 

 upon the broad-leaved hosts. Neither of these spore-forms is 

 able to reinfect the same host on which it was produced, but 

 must pass to the alternate host. The association of the two 

 kinds of hosts is, therefore, necessary for the spread of the 

 disease from one tree to another. 



The leaves and young branches of the junipers and cedars 

 are infected by spores from the alternate host. During the 

 second season after infection abnormal overgrowths appear in 

 the form of swellings of the branches and trunk, witches'- 

 brooms (i.e., compact clusters of small branches), or trans- 

 formations of the leaves into galls commonly known as "cedar- 

 apples" (Fig. 21). In a few cases no overgrowths are developed, 

 the only visible symptoms being a yellowing of the leaves. 

 The "cedar-apple" type of abnormality is most frequent upon 

 the red-cedars and junipers which are used for windbreaks or 

 for decorative planting in yards and gardens in the proximity 

 of orchard trees. The spores of this stage are produced upon 

 these diseased parts in the spring. 



In the case of the broad-leaved hosts, the leaves and fruits 

 are attacked in the spring. Small localized spots of a yellowish 

 color appear, and later long whitish tubes of fungous material 

 are pushed out all over the surface of these spots. Within the 

 tubes, the spores which are able to infect the coniferous hosts 

 are produced. 



