ROYAL BOTANIC GARDENS, KEW. 



BULLETIN 



OF 



MISCELLANEOUS INFORMATION. 



No. 1.] 



[1907. 



I. -PLANT DISEASES. - VII. "CLUSTER-CUP" 



DISEASE OF CONIFERS. 



(Cah/ptospora Goeppertiana, Jul. Kiihn.) 



(With Plate.) 



G. Massee. 



The term "cluster-cup" is used popularly in this country 

 to designate the Aecidium-form of fruit of many of the "rusts'" 

 or Uredines. It appears in the shape of tiny white cups with 

 frilled edges, filled with yellow spores, growing in dense clusters 

 on the living leaves of many of our wild and cultivated plants. 

 The fungus causing this disease is one of those parasites which, 

 when opportunity offers, grows on two different kinds of host- 

 plant during different periods of its development. The resting- 

 spore stage grows on Vaccinium, and the " cluster-cup " stage on 

 various conifers. 



It has been proved, however, that when conifers are not forth- 

 coming, the " cluster-cup " or Aecidium-stage can be left out of the 

 cycle of development of the fungus, which continues to reproduce 

 itself entirely on its Vaccinium host. On the other hand when 

 Vaccinium and conifers grow together, the fungus certainly passes 

 from the former to the latter, and often proves very destructive 

 to young trees and nursery stock, causing defoliation early in the 

 season. It may be mentioned that in some other "rusts" or 

 Uredines, to which group the present fungus belongs, the 

 Aecidium- or "cluster-cup" stage may drop out without in any 

 way interfering with the continuation of the species. This 

 frequently happens in the case of a rust of wheat— Puccin ia 

 graminis, DC. In many other rusts the "cluster-cup" stage has 

 been permanently left out of the cycle of development. 



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