512 FROMME: THE CULTURE OF CEREAL RUSTS 
pustules on the second leaves was due to the fact that only their 
tips were exposed at the time of inoculation. The number of 
pustules on the upper and lower surfaces of a leaf is sometimes 
equal and two pustules are often situated directly opposite each 
other. The average number of pustules per plant maintained in 
the mass culture experiments was about 200-300. The lowest 
average recorded for a culture was 161.6, the largest 598.7. The 
largest number of pustules counted on a single plant was 996 
(plant 3, TABLE II). 
TABLE II. 
ANALYSIS OF INFECTION ON CULTURE 7C 
Treatment: Innoculated by dry spore method, covered with bell jar. Number 
of plants, 72. Date planted, January 1. Date innoculated, January 13. Date of 
sporulation, January 24. 
Number of parts Part of plants No. of parts infected Per cent. infected 
72 First leaves ie 100 
72 Second leaves 45 62.5 
72 Leaf sheaths 2I 29.1 
— 
NUMBER OF PUSTULES ON TEN PLANTS SELECTED AT RANDOM 
No. of ; First leaves Second leaves 
plant SIME MEE eee oe : Leaf Total, entire 
Lower surface | Upper surface Sane haa rend — 
207 246 27 30 I 601 
2 215 341 12 2I 5 594 
3 506 441 18 31 o 996 
4 444 521 7 II ms 986 
5 234 336 4 5 0 579 
6 225 249 0 o ts) 474 
7 376 403 10 13 3 805 
8 99 140 oO oO 2 241 
9 53 TI5 I 3 ° 172 
Bae) 189 314 I4 22 is) 539 
Total 2638 3106 93 136 14 5987 
Ave...... 263.8 310.6 9-3 13.6 1.4 598.7 
Ave. 574.4 22.9 1.4 598.7 
NORMAL DEVELOPMENT OF THE UREDOSORI OF P, CORONIFERA 
The period of incubation for the rust in the open greenhouse 
varied between eight and eleven days from October to December. 
Twelve days was the constant incubation period during December 
but this decreased to nine days in the latter part of January and 
