[VoL. З 
58 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
plants were set in the field June 24. The disease was begin- 
ning to show on July 8, when only 0.05 per cent of the plants 
were yellowed, and increased rapidly to 40.5 per cent on July 
29. Of 420 plants set on July 15, after the hottest weather 
had passed, all remained healthy to August 21, but on account 
of the late planting did not make heads, and, therefore, were 
not considered later. The curves given in fig. 13 show the re- 
lation of the occurrence of the disease to temperature. The 
temperature data from whieh these were plotted are those pub- 
lished by the Milwaukee office of the United States Weather 
Bureau, a distance 25 miles north from the experimental field. 
TABLE VII 
SUMMARY OF FIELD OBSERVATIONS ON EXPERIMENTAL PLOT AT 
RACINE, WISCONSIN, 1912 
July 16 July 22 August 20 
Total Ке МИМИ! 
Strain no. o 
plants | Number | Per cent | Number | Percent | Nu mber | Per cent 
yellow | yellow | yellow | yellow | yellow yellow 
СТР ЕРА 45 18 4.0 32 n. 37 82.2 
|]: EDENDI 45 3 6.6 24 GR 32 71.1 
TU SE 44 2 54.5 35 79.5 43 95.4 
VII (a-y)...... 1039 284 27.3 551 3.0 567 54.6 
VIII (a & b)... 89 1 Ij 21 3.5 11 12.3 
IX (8-116)..... 352 31 8.8 13 6.9 191 54.3 
X (101-143).... 625 97 15.5 195 1.2 234 37.4 
i S 43 12 27.9 27 62.8 32 74.4 
BE 39 5 12.8 18 46 17 43. ( 
4 EE 29 8 27.6 19 65.: 20 68.9 
ТОШ» 2350 185 20.5 1052 40.5 1184 50.3 
Again, in 1913, observations were made in the field on the 
same plot. The results of these observations are given in 
table уіп and fig. 14. Besides the strains used in 1912 sev- 
eral new commercial sorts were introduced. Strains XIII 
and XIV were Danish Ball-head bred locally, XIII being short- 
stemmed and XIV long-stemmed; strain XVI was Danish 
Ball-head grown by the Ferry Seed Company; XVII was All 
Season; XVIII, Succession; XIX, Volga; XX, Harly Jersey 
Wakefield; XXI, Copenhagen Market; XXII, Early Summer; 
XXIII, Charleston Wakefield. While the experience of the 
