57^ Journal of Agricultural Research voi. xxvi, no. 12 
Table I .—Comparative size of host nuclei and of plastids in or near infections of Puccinia 
graminis tritici form III of different ages on seedlings of Baart wheat a 
A. TISSUE IN OR SURROUNDING AN INFECTION 
Days after inoculation. 
Center of Center of 
Margin of 
Margin of 
Adjacent 
infection, uredinium. 
uredinium. 
infection. 
uninfected 
tissue. 
Normal or 
nearly nor¬ 
mal tissue. 
HOST NUCLEI 
2SL . 
7a. 
140X90 
136X98 
I29X9 1 
135X94 
110X84 
107X82 
146X43 
102X70 
114X84 
113X71 
107X82 
145X49 
111X80 
113X68 
113 X90 
7b.. 
10a. 
143X116 
126X75 
141X42 
159X123 
128X109 
120X38 
10b. 
113X82 
110X80 
14a. 
PLASTIDS 
38X17 
41X26 
43X23 
40X21 
25X14 
20X14 i 
39X24 1 
52X25 
53X24 
22X15 
27X20 
41X23 ; 
1. 
44X27 
28X20 
37X20 
32X26 
33X23 
45X24 
1. 
60X25 
57 X 25 
60X26 
40X25 
4 IX2I 
46X20 
B. TISSUE IN AND BETWEEN TWO NEIGHBORING UREDINA 
Days after 
inocu¬ 
lation. 
Center of 
first 
uredinium. 
Margin of 
first 
uredinium. 
Mycelium 
somewhat 
sparse. 
Midway 
(very few 
hyphae). 
Mycelium 
somewhat 
sparse. 
Margin of 
second 
uredinium. 
Center o 
second 
uredinium. 
HOST NUCLEI 
IOC. 
14b. 
148X115 i 127X115 
142 X 45 ! 169 X 48 
1 
127X112 
I 5°X 53 
117X98 
148X58 
124X111 
136X 56 
1 i 
i 142X115 ! 142X117 
136X 51 I 140X 56 
PLASTIDS 
IOC. 
14b. 
34X22 
41X23 
35X21 
46X23 ! 
30X21 
37X19 
31X24 | 
37X18 j 
26X17 
40X19 
37X25 
42X21 
40X25 
50X22 
a Each figure given represents the sum in millimeters of the diameters of io nuclei or io plastids X 1130. 
The history of the plastids in the outlying portions of the infection 
area is less simple. As early as the seventh day after inoculation the 
influence of the fungus has extended for a short distance beyond the tips 
of the outer hyphae. The reduction in plastid size is slight (52 by 25) but 
unmistakable. Ten days after inoculation (Table I, A, plastids, 10a and 
10b) the plastids at the margin of the infection, 25 by 14, and a consider¬ 
able distance beyond it, 22 by 15, are reduced in size far below those at 
the center of the same infection. Even at the end of the section, some 
