GYMNOSPORANGIUM. 401 



A sharply defined roundish scar of a light-yellow colour 

 remains after the spores are cast. This is composed of a 

 superficial layer of coloured pseudoparenchyma, with an under- 

 lying scar-tissue of characteristic constitution. The latter con- 

 sists of several layers of cork-cells extending from one edge of 

 the scar to the other, separating the cushion from the twig- 

 tissues. This scar-tissue is not broken through next year, but 

 the new sporogenous cushions break out through other parts 

 of the bark (Fig. 236). 



G. confasum Plowright.^ (Britain.) This is found on 

 Juniperus Sabiiia along with G. sdbinae, from which it is 

 difficult to distinguish. Pycnidia and aecidia are produced 

 generally on Crataegus Oxn/acantha and Cydonia vulgaris, rarely 

 on Pyrus communis. The aecidia on Crataegus resemble those 

 of G. clavariaeforme on the same host, and dehisce by the 

 ruptured apex of the peridium. Those produced on Pyrus 

 communis are distinguished^ from aecidia of G. sabinae on 

 the same host by dehiscing through the open apex of the 

 peridium. 



Infections of Gym. confusum from Juniperus communis gave 

 the following results : 



On Host-plant. Authority. 



C<^donza vulgaris, {^^tubutr peridia!"'^''' "^"'^ l^" ^''"^^'■- 

 Crataegus Oxyacantha, „ „ „ „ 



Pyrus communis, „ „ „ „ 



Crataegv^ Oxyacantlia, „ „ „ Plowrifflit. 



The following American species of Gymnosporangium have 

 been described:^ 



On Arborvitae or white cedar: 



G. biseptatum Ellis. On twigs and needles of Chaonaecyparis 

 thyoides and Zibocednis decurrens. The aecidia on Crataegus 

 tomentosa and Amelanchier canadensis. 



' Plowright, Linnean Soc. Journal {Botany), 1887. E. Fischer, Zeitschrift /. 

 Pflanzenlcrankheiten, i., 1891 ; with summary of literature. Klebahn, Forstl.- 

 naturwiss. Zeitschrift, ii., 1893. 



''E. Fischer (loc. cit.). 



^Farlow, The Development of the Oymnosporangia of the United States, 1886, 

 and other papers. Thaxter in various papers on Oymnosporangia, 1886 to 

 1891. Halsted (Repm-t on Vegetable Pathology for 1888, U.S. Dept. of Agri- 

 culture) gives a resume, with description and figures of G. macropus and 

 treatment for orchard-rust. Fischer, Zeitschrift f. Pfianzenhranhheiten, i., 1891. 



2C 



