DISEASES OF PLANTS. 



80 



the other hand, when a juniper is once infected, the mycelium is 

 perennial in the branch, and produces a crop of fruit each spring 

 without any further inoculation. 



Fig. 5. — Peak Leaf Cluster-Cup (Gymnosporangmm Sabince). 



(1) The spring form of fruit growing on juniper ; one-quarter natural size. (2) A single 

 spore of the spring form growing on juniper ; magnified 300 times. (3 and 4) The summer 

 or cluster-cup form of fruit growing on living pear leaves ; half natural size. (5) Two 

 cluster-cups ; (A) closed, (B) cut open to show the spores in its interior ; slightly magnified. 

 (6) Spores from a cluster-cup ; magnified 300 times. 



As it is absolutely necessary for the existence of this fungus 

 that it should spend part of its time on a juniper, and part on a 

 pear tree, it is obvious that if one of its two host-plants is 

 removed the disease would cease to exist. A single diseased 

 juniper is quite sufficient to infect all the pear trees growing in 

 its neighbourhood ; therefore, if the disease shows itself, seek 

 out the juniper, and remove it altogether. If that is not desirable, 

 the infected branches should be cut away. These are readily 

 recognised by the gouty swellings caused by the fungus, as well 

 as by the gelatinous masses of the fungus itself projecting from 

 cracks in the bark. 



Several other rosaceous plants, as hawthorns, apples, &c, 

 have their leaves and fruit attacked by cluster-cups, one stage of 

 which also develops on species of juniper ; hence the suggestions 

 given above will suffice for the removal of the parasite. 



