390 
Journal of Agricultural Research 
Vol. XXI, No. 6 
VARIATION IN DEVELOPMENT OF INFECTION 
The normal development on the more susceptible varieties, of which 
Tennessee Green Pod is an example, is described as follows from inocula¬ 
tion made on January 20, 1919. The inoculation was made at 5 p. m., 
and after 24 hours in the moist chamber the plants were placed on the 
greenhouse bench. The first evidence of infection was noted 136 hours 
after inoculation. The sori at this time were very faint indeed, being 
scarcely visible. In 143 hours they were evident on close examination 
as minute pale spots. They were quite distinct after 161 hours, had 
taken on a pale yellow color, and were slightly elevated above the leaf 
surface. At 183 hours the centers of the sori were orange-red in color, 
showing sporulation, and were conspiciously elevated. The epidermis 
had ruptured on some of the larger sori in 190 hours, and the uredinia* 
spores were exposed. A ring of secondary sori develops around the 
primary sorus on the more susceptible varieties. 
Variations from the normal development are found in a number of varie¬ 
ties. These variations may be listed as follows: (a) production of flecks, (b) 
production of telia instead of uredinia, or sori containing both uredinio- 
spores and teliospores, (c) production of uredinia subnormal in size, (d) 
lengthening of incubation period. 
The term fleck is used to indicate an abortive infection. The flecks 
produced on different varieties vary somewhat in shape and size (PI. 73, 
A, B). The flecks which develop on Tennessee Wonder (PI. 73, C) are 
seen on both leaf surfaces, but are most conspicious on the lower surface. 
They are circular in outline, with a slightly irregular border. The spot is 
concave, the tissue being noticeably shrunken. A definite bronze-brown 
rim bounds the fleck. This is narrow in some flecks and may extend 
well toward the center in others. An island of green tissue may remain 
in the center, and this may protrude slightly, suggesting the beginning 
of a sorus. In some varieties a small sorus is developed in the center of 
some of the flecks (PI. 69, B, e, /). The flecks on any variety are usually 
larger than the sori, their average diameter being from two to three 
times that of the sori. 
The development of flecks is characteristic of certain varieties and is 
considered an indication of resistance. No flecks have ever been seen on 
Tennessee Green Pod or other very susceptible varieties, but they are 
regularly produced on certain others, notably Tennessee Wonder, Im¬ 
proved Goddard, and Hodson Green Pod. On some varieties all the 
infections develop into flecks, while on others there may be a considerable 
number of normal sori developed and only a few flecks. The percentage 
of flecking with the different varieties is shown in Table III. 
