THOMAS: INFECTION OF APIUM GRAVEOLENS 21 
a second record five days after the first showed an average increase 
of fifteen spots per plant on the plants of the lower temperture. 
One set of plants showed a consideraby higher count on the 
plants of lower temperature after thirty-six days. The results 
are too variable to be in any way conclusive. A factor of probably 
greater importance is the fact that the host plant may be more 
vigorous and make its greatest growth in cool weather with the 
autumn rains. Rolfs (32) states that in Florida celery can be 
grown only as a cool weather crop. Lloyd (20) and Watts (41) 
point out that celery demands cool weather, at least cool nghts, 
for satisfactory growth. However, I have not found any specific 
data to show the optimum temperature for the culture of celery. 
RELATION OF AGE TISSUE TO INFECTION 
The absence of any conspicuous sign of infection in the field 
during the early and middle parts of the growing season led the 
earlier workers to believe that young plants were affected only 
slightly or not at all. The more careful observations of later 
workers have already disproved this. I have observed the fungus 
on plants in the various stages from the seed bed to maturity. 
TABLE XII 
NUMBER OF SPOTS ON LEAVES OF DIFFERENT AGES TWENTY-SEVEN DAYS AFTER 
INOCULATION 
Leaf No.* I | 2 = | 4 5 | 6 7 | 8 | 9 | 10 
Plant No. t,o. 00 ts ee ee ) | o | 18|209/254| 75| 17| so| | 
” 2c oe eee et dae pee ae dat ee 193 | 61 79 | 
SN Se ee 0/90 5 93 | 185 | 127 44} 41 
az Ay oe ee ee 0/0 QO} 40] 95; 136| 26 25|24| 4 
ie BOP Poise bee ee |oj}o $2) 426 | 36| 27| 11 Pon 
es Oe eee ae 0 | 0} 39F104| 42] 67| 31] 9} 
| 
OTE A ED oan Men onee peeseee none ae 0 | 0 | 149| 945' 673! 511! 129 | 125| 241 4 
In the field a row of young plants was set out on July 17 so that 
they were about half grown when the infection was becoming 
severe on the regular crop (late September). Counting the number 
of spots per leaf is not practicable under field conditions but it 
was obvious that these young plants were attacked with a 
severity quite sufficient to throw doubt on the idea of a close 
* The | bered here from the center of root crown outward, i.e., from 
youngest to oldest. 
