

A 'CLUSTER-CUP' DISEASE OF CONIFERS xix 



plants, and many are numbered amongst the most destruc- 

 tive of fungus parasites. ' Cluster-cups ' appear under the 

 form of clusters of minute white warts on living leaves. 

 These warts eventually burst open at the top and present 

 the appearance of minute cups with toothed edges curled 

 outwards, and are filled with bright orange powder which 

 in reality consists of myriads of spores. The spores from 

 ' cluster-cups ' are scattered by wind and infect some other 

 kind of plant, and the resulting fungus presents a very 

 different appearance to the 'cluster-cup' form, although 

 in reality it is a portion included in the life-history of the 

 'cluster-cup.' 



During recent years silver fir (Abies pectinatd) has 

 suffered from the attacks of Calyptospora. One stage of 

 the fungus grows on the Cowberry ( Vaccinum vitis-idaea\ 

 causing the stems to become much thickened and spongy. 

 Such diseased stems are at first rosy-pink in colour, 

 gradually changing to deep brown. Diseased Cowberry 

 plants grow much taller than healthy plants, all the 

 branches are quite erect, and the leaves are much 

 dwarfed. If conifers happen to be growing in the neigh- 

 bourhood of diseased Cowberries, and spores from the 

 latter are carried on to the surface of young conifer leaves, 

 they become infected, and within three or four weeks after 

 infection two rows of cylindrical white cluster-cups appear 

 on the under surface of the conifer leaves. The spores 

 from the cluster-cups will infect Cowberry plants, but 

 will not directly infect other conifer leaves. On the other 

 hand, in the absence of conifers, the disease can continue 

 to reproduce itself on the Cowberry alone. 



When conifers are attacked almost every leaf is infected. 

 Such leaves turn yellow and fall early. If this happens 



