1032 
Journal of Agricultural Research 
Vol, V, No. 33 
The averages for the eight leaves mentioned are: 
Leaf No. 
• 
Size of leaves. 
Number of stomata. 
Length of stomatal 
pores. 
Number 
of leaf- 
Length. 
Width. 
Upper. 
Lower. 
Upper. 
Lower. 
spots. 
I to 4. 
Cm. 
14.6 
12.6 
Cm. 
II 
9 1 
120. 6 
II7. 2 
164. I 
Cm. 
19 
16. 7 
Cm. 
19 
l6. 2 
20 
8 to 11. 
10.6 
2 
It is also to be noted that infected leaf n, which had only one spot, 
had the shortest average stomatal pore lengths (except leaf 9) and the 
highest number of stomata per area of any of the infected leaves studied. 
From these figures it would further appear that of all the uninfected 
leaves studied, only leaf 1 would have a stomatal count and pore length 
that would indicate leaf susceptibility. It might be concluded that this 
leaf remained uninfected merely by chance and that the others were 
uninfected because they had not as yet reached the maturity which would 
allow infection to occur. 
Detailed field observations made of the amount of infection that ap¬ 
peared on the different leaves of many sugar-beet plants during an entire 
season have again shown that the greatest number of leafspots developed 
on the mature leaves. The records from one plant are shown in Table 
XI. The leaves were tagged and numbered consecutively, beginning with 
the outermost, or oldest, so that the new leaves tagged on all days 
after the first one were heart leaves. As these grew older they became 
susceptible to leafspot, and with increased maturity usually became 
heavily infected, and finally the death of the leaf occurred. Those leaves, 
whose numbers are in italic, on the last date reported were killed by the 
fungus. From 400 to 1,000 spots were sufficient to kill a leaf, depending 
on its size, in a few days. While the death of many of the leaves not 
reported as killed by Cercospora beticola was no doubt hastened by the 
presence of the fungus, yet age and other factors were predominating 
causes of the death of the leaf. 
The results obtained show that, as a rule, infection did not take place 
readily on old yellow leaves, but occurred most readily on active green 
leaves. It is true that there was often a large increase in the number 
of spots present on the leaves during the few days just previous to the 
death of the leaf, as is shown by leaves 21, 24, 25, 27, 35, and others on 
this one plant (Table XI), but such leaves were not normally old. They 
were no doubt green and quite active when infection took place and 
merely died prematurely and very suddenly as a result of the great 
number of spots produced. 
