1030 
Journal of Agricultural Research 
Vol. V, No. aa 
Table IX. — Effect of light and medium on the germination of conidia of Cercospora 
beticola , at a temperature of 24 0 C., on August 12, IQI3, at Rocky Ford , Colo. 
Environment. 
Number 
of hours 
of growth. 
Average 
percent¬ 
age of 
germinat¬ 
ing 
conidia. 
Average 
number 
of cells 
per co- 
nidium. 
Average 
number 
of germi¬ 
nating 
cells per 
conidium. 
Average 
length of 
germinat¬ 
ing tube. 
Distilled water, north light. 
Distilled water, dark room. 
6X 
6H 
8 
IOO 
100 
2. 47 
2 . 4 
/* 
43.28 
41.11 
5 6 - 3 r 
Distilled water, north light. 
100 
9. 42 
4.14 
Distilled water, dark room. 
8 'A 
IOO 
8. 69 
3 - 46 
65 - 77 
Bean decoction, north light. 
9 
IOO 
9. 44 
3-33 
SS -48 
Irrigation water, north light. 
9H 
IOO 
IO. 16 
3-83 
91.69 
Soil decoction, north light. 
IO 
IOO 
6 
3. 00 
98.42 
Germination also occurred equally well in distilled water, bean decoc¬ 
tion, soil decoction, and irrigation water, showing that a nutrient medium 
did not hasten germination nor did it retard it. It is also to be noted 
that the conidia were incubated nearly twice as long in soil decoction as 
in distilled water, which would account for the longer germ tubes in the 
soil decoction. In both solutions 100 per cent of the conidia germinated. 
The condensed moisture that may be found on leaves then would seem 
to give a favorable medium for conidial germination and that germ- 
tube growth could take place rapidly in it. It has been found that 
only a short time is necessary for germination to take place, since newly 
formed conidia may begin to germinate in three hours after being placed 
in water cultures at 26° C. The germinating tubes from such conidia 
may increase 5ju in length in 40 minutes. 
The effect of high temperatures on conidial germination is not con¬ 
sidered in this discussion. However, in another phase 1 of the study of 
the sugar-beet leaf spot, it has been determined that a period of days with 
extreme high night (70° F.) and day (104° F.) temperatures together 
with low relative humidity, a condition that may occur at times in an 
irrigated region, is inimical to the life of the conidia. This factor then 
becomes of importance in considering conidial growth and development 
under natural environment. 
LEAF MATURITY 
Near the middle of the summer or later, in a sugar-beet field infected 
generally with leafspot, the individual plant presents a typical picture of 
the disease. A cluster of uninfected heart and slightly infected young 
mature leaves occurs at the center of the plant, while all other leaves 
on the same plant are heavily infected. A comparison was made of the 
stomata on such heart and young mature leaves, or the oldest uninfected 
and the youngest infected leaves, on each of several plants. The study 
1 The thermal relations of the fungus will be discussed in a later paper entitled * ‘ Relation of climatic 
conditions to infection by Cercospora beticola.” 
