BLACK KNOT 



139 



if not equally so, and conidia or spores from any species 

 of tree infested appear capable of inoculating any other 

 species ; hence the work of extermination of diseased trees 

 must extend to wild as well as cultivated forms, and, 

 furthermore, to ensure success, the movement must be 

 general, experience having shown that it is of comparatively 

 little use attending thoroughly to your own trees if your 

 neighbour fails to follow suit. Legislative measures have 

 been pressed into force in some of the States in the United 

 States for the purpose of endeavouring to enforce this 

 object. 



Farlow, Bull. Bussy Inst., 1875, 3 pi- 

 Halsted, N. Jersey Agric. Coll. Expt. Station, Bull. 78 

 figs. 



Ploivrightia ribesia, Sacc. Occurs on living branches 

 of red and black currant and gooseberry. Black patches 

 are formed under the epidermis, through which the small 

 black clusters of perithecia protrude, resembling rough, 

 black warts. 



HYSTERIACEAE 



PINE LEAF-CAST 

 (Lophodermium pinastri, Chev.) 



A tiny fungus, producing very minute, elliptical, black 

 spots on the leaves of various species of pine, causing the 

 leaves to fall prematurely, and consequently, especially in 

 the case of seedlings and young trees, finally killing the 

 plant. The following is abridged from Hartig's detailed 

 account of the disease : 



