CAUSE OF THE DISEASE. - 11 
quite variable in size, those which develop in corn-meal cultures being 
rather large, while those on leaves are comparatively small. Average- 
sized pycnidia have a diameter of about 0.5 millimeter, but the range 
of size runs from 0.1 to 1 millimeter in diameter. 
A cross section of a pyenidium (fig. 1) shows a dark outer layer of 
large-celled pseudoparenchyma; 
inside this is a thick, lighter col- 
ored layer of rather loose texture, 
making up the bulk of the pyeni- 
dial wall; next is a densely woven 
olivaceous or brownish layer, and 
within is a closely woven hyaline 
layer. The interior of the pyc- 
nidium is usually more or less 
plurilocular through the upward 
growth or invagination of the 
base or by an inward protrusion 
from the side. 
The spore masses when mature 
are extruded either in an indefi- Fic. 1.—Section through a pycnidium of Phomopsis - 
nite cream-colored or yellowish en 
mass or in slender ropelike masses from 1 to 3 centimeters long. 
(Pl. III, fig. 2.) 
The spores are of two kinds: Those called by Diedicke! « spores are 
spindle shaped or nearly so, measure 7 to 10 by 3 to 4 », mostly 
8 by 3 », contain two oil drops, and are borne on cylindrical basidia 
measuring about 20 by 2.5 y (fig. 
Sa ERSET SA 2). They germinate readily in 
MS, distilled water. 
re Those which Diedicke desig- 
() nated as £ spores and called by 
ey, ak Shear scolecospores are threadlike, 
( curved at the center, hooked at 
cs one end, sigmoid or nearly straight, 
i somewhat attenuated and borne 
Fic. 2.—The two forms of spores of Phomopsis mali ON short, conical basidia. They 
produced in one pycnidium. : = cC 
: vary considerably in size, the 
average being 28 by 1.5 ». Repeated attempts have been made to 
germinate these spores, but without success. 
A pyenidium may produce spores all of one kind, but usually both 
kinds are found in the same pycnidium, though there is often a 
greater quantity of the one than of the other. Pycnidia developed 
on leaves show less tendency to form the long, curved sort than 
1 Diedicke, H. Die Gattung Phomopsis. Annales Mycologici, V.9, p. 8-35, pl. 1-3, 1911. 
280 
