Apr. IS, I9I5 Phoma Destrtictiva 15 



Irish-potato agar. — Whitish myceUal growth appears within two to 

 three days. At first cottony in appearance, it later forms a compact 

 mat of hyphal threads. In 5 to 7 days the medium darkens, and in 10 

 days pycnidia and spores have developed. Pycnidia develop more slowly 

 and less abundantly upon this medium than upon the string-bean, 

 prune, or oat agars. 



String-bean agar. — Round whitish fungous colonies appear in two 

 to three days. A few days later the surface growth becomes a compact 

 mat, neutral gray in color, beneath which lies a darker substratum con- 

 taining the pycnidia. Mycelial growth is more abundant than on beef 

 agar, and the colonies are fuller, with somewhat convex surfaces. Pyc- 

 nidia form within 6 to 10 days and within 10 to 14 days an exudate may 

 be seen at the apex of the pycnidium, at first in the form of drops and 

 later as a thick slime overspreading the surface of the culture. 



Lima-bean agar. — A whitish cottony growth appears within three to 

 five days and a few days later pycnidia form, causing a darkening of the 

 substratum. The pycnidia are round to irregular in outline, separate 

 or in clusters, and show the characteristic slimy exudate. 



Prune agar. — In two to three days there is a whitish fungous growth, 

 which a few days later becomes grayish green in color. Single hyphae 

 when examined under the microscope appear olive green. These hyphae 

 contain numerous oil drops which disappear when treated with ether. 

 With pycnidial development a dark, almost black color is produced in 

 the substratum, while the spore exudate forms a slime on the surface. 



Oat agar. — An abundant mycelial growth develops within three to 

 five days. Later this growth darkens as a result of pycnidial develop- 

 ment and there is an abundant spore production. 



Synthetic agar.^ — A scant mycelial growth develops within three to 

 five days, at first whitish but later becoming neutral gray in color. 

 Spore development is poor. 



Sterilized potato cylinders. — Within two to three days a whitish 

 mycelium develops upon the surface of the potato plant. As growth con- 

 tinues, the mycelium becomes compact, varying in color from Ridgway's^ 

 neutral gray to mouse gray. With the development of pycnidia the sub- 

 stratum darkens and at the end of two weeks the growth becomes dark 

 and feltlike, showing drops of exudate on the surface. Six-weeks-old po- 

 tato cultures become carbonaceous in appearance and soot-black in color. 



Sterilized cotton stems. — Upon this medium there is scant mycelial 

 growth in four to five days. Later the stem becomes covered with a dark 

 growth consisting of hyphal threads, dark pycnidia, and spore masses. 



Sterilized sweet-clover stems (Mdilohis alba). — A scant grayish 

 white mycelium develops upon the surface of the stem. Later the sub- 



' Darwin, Francis, and Acton, E. H. Practical Physiology of Plants. 321 p., illus. Cambridge, 



England, 1894. 



"Ridg-way, Robert. Color Standards and Color Nomenclature ... 43 p., 53 col. pi. Washington, 

 D. C, 1912. 



