ROSE CANKER AND ITS CONTROL. 



37 



Sugar Gelatin. 



C. scoparium. 

 Rank growth of coarse radiating 

 aerial mj-celium, but few spores. Gela- 

 tin liquefied. After about four days a 

 striking brilliant carmine color begins 

 to appear in reverse, due to a pigment in 

 the gelatin. This gradually spreads to 

 the whole plate and becomes darker, an 

 ox-blood red. This is probably the best 

 diagnostic cultural character for this 

 species. The mycelium covers the 

 plate in ten days. 



C. parvum. 

 Fine tangled aerial mycelium and 

 more abundant spore production than 

 for C. scoparium. Gelatin liquefied. 

 Covers entire plate in two weeks. At 

 the end of a week the colonies vary from 

 Mars yellow to raw sienna in reverse, 

 and at the end of two weeks have darkened 

 to amber brown and Mars yellow. The 

 color during the entire development of 

 the colony is in strong contrast to the 

 carmine and ox-blood of C. scoparium. 



Czapek's Agar. 



C. scoparium. 

 Growth moderately good, aerial 

 mycelium thin. Spores abundant. At 

 the end of a week the colors in reverse 

 are much the same as for potato agar, — 

 claret brown, russet or amber, with a 

 brick-red color suffused through it. At 

 the end of two weeks the center is prac- 

 tically black, fading through broivn and 

 red tints toward the margin. The red 

 color is due to a pigment in the me- 

 dium; the brown, to the chlamydo- 

 spores and sclerotia. Irregular edge. 



C. parvum,. 

 Finer and denser aerial growth of 

 mycelium. During the first week the 

 reverse remains pearly white; later it 

 changes to dilute wood brown, then Rood's 

 brown and at the end of two weeks ap- 

 proaches Natal brown. None of the 

 red tints of C. scoparium ever appear. 

 Margin much more even than that of 

 C. scoparium. Abundant production 

 of spores in distinct concentric zones. 



Latin Description of Cylindrocladium parvum. 



Cylindrocladium parvum n. sp. Album effusum; conidiophoris 

 erectis, base simplicibus, apice ternate vel dichotomice ramosis, 130 x 4-^5fj-; 

 conidiis cylindraciis, medio obscure 1-septatis, hyalinis, 16.8 x 2.5/^. 



Hab. in caulibus emortuis et radicibus rosarum et in humo, Massachu- 

 setts in A^ner. bor. — Simile C. scopario. 



CONTROL. 



Every method used in the control of an}' fungous disease is an appli- 

 cation of one of four principles: (1) exclusion of the fungus, (2) eradica- 

 tion of the fungus, (3) protection of the host, or (4) immunization of the 

 host. Although practically all the work of the present investigation 

 has been on the second of these principles, there are possibilities of using 

 all four of them in the control of rose canker. These four are first con- 

 sidered separately below in the order named, and finally a general scheme 

 of treatment is recommended. 



