298 PLANT DISEASES 



destroyed by the pest named above. Two-year-old shoots 

 are only very rarely infected. In the month of May the 

 periderm of diseased shoots is ruptured at intervals longi- 

 tudinally, exposing the conidial layer of the parasite as a 

 greyish-green cushion, bounded by the upraised periderm. 

 Young shoots are infected in May and June by the conidia 

 before the periderm is formed, and such usually perish the 

 following season. 



PREVENTIVE MEANS. Hartig states that the disease can 

 be prevented by removing the diseased shoots from the 

 crown in the beginning of May. 



Hartig and Somerville, Diseases of Trees \ p. 141, fig. 80. 



HYPHOMYCETACEAE 

 MUCEDINEAE 



(jOospora abietum, Oud.) 



Defoliation of various conifers Abies excelsa, A. pinsapo, 

 A. nordmanniana, and A. douglasii results from the injury 

 done by an inconspicuous fungus called Oospora abietum. 

 A single row of minute greenish-grey fluffy tufts on each 

 side of the nerve, and on both surfaces of the leaf, come 

 to the surface through the stomata; the delicate hyphae 

 composing these tufts produce minute, colourless, elliptical 

 conidia, which, being scattered by wind or rain, alight on 

 other healthy leaves and spread the disease. 



PREVENTIVE MEANS. It is advised that all fallen leaves 

 should be collected and burned. 



Oudemans, Compt. Rend, de FAcad. Roy. d. Sa. des Pays- 

 Bas, seance de Jan. 1897. 



