426 
Journal of Agricultural Research 
Vol. XXIX, No. 9 
with a suspension of spores in sterile 
distilled water and then placed in a 
large moist chamber for about 48 hours. 
The leaves were first rubbed gently to 
remove the waxy bloom so that the 
spore suspension would stick. Like¬ 
wise, the heads of cabbage and the 
Curds of cauliflower were sprayed with 
a suspension of spores and then placed 
in moist chambers, usually battery 
jars lined with wet filter paper, and 
incubated at different temperatures. 
Heads and leaves of cabbage and cauli¬ 
flower growing in the field were sprayed 
with a spore suspension and then the 
outer leaves were pulled up and tied 
about the head. Controls which con¬ 
sisted of plants from the same lot, 
treated in every way the same as those 
inoculated except that spores were not 
permitted to come in contact with 
them, were held in each experiment. 
Usually isolations were made from 
the lesions formed on the inoculated 
host parts. In some instances a micro¬ 
scopical study was made which showed 
the typical Alternaria spores to be 
present in great abundance on the 
lesions. The organism isolated was 
shown to be capable of infecting a 
healthy host and producing the typical 
symptoms. 
The results of several of the inocula¬ 
tion experiments are tabulated in 
Table II. A high percentage of infec¬ 
tion was obtained in all cases. The 
number of spots produced on the heads 
and leaves varied from a few to very 
many, depending largely on the humid¬ 
ity and on the concentration of the 
spore suspension used. For the most 
part the leaves seemed more susceptible 
than the heads under field conditions, 
although a large number of infections 
on the latter were obtained. No inju¬ 
ries of any kind were made intentionally 
or could be observed on the curds of the 
cauliflowers before inoculation. 
The experiments listed in Table II, 
together with those given in connection 
with temperature studies later, show 
conclusively that the species of 
Alternaria commonly associated with 
the leafspot and brownrot lesions is 
capable of producing such lesions under 
the conditions existing in these experi¬ 
ments. Other species of Alternaria 
were frequently found growing sapro- 
phytically on decaying cauliflower and 
cabbage. The fungi numbered 5089, 
5095, and 4866a in Table II proved to 
be of this nature. Not only did these 
prove to be nonparasitic but they dif¬ 
fered morphologically from the para¬ 
sitic forms, all of which were alike. 
On the plants in the greenhouse 
which were inoculated on February 22, 
1922, infection was evident as very 
minute dark-brown spots just visible to 
the unaided eye in 48 hours, when they 
were removed from the moist chamber. 
These spots were so numerous on some 
leaves that two-thirds or more of the 
entire leaf surface was involved. When 
examined 24 hours later, the large green¬ 
ish water-soaked type of lesion was 
present and large areas of the leaves 
were killed. A similar condition is 
illustrated in Plate 2, C. The dead 
tissues later turned light brown in 
color and had a papery texture. Five 
days after the inoculations were made 
some of the petioles were so badly 
decayed that they broke off. Like¬ 
wise, the laminae of some of the leaves 
were so severely affected that the leaves 
dropped off. So large a number of 
infections probably seldom, if ever, 
occurs on a host under natural condi¬ 
tions, yet one-half to two-thirds of the 
laminae of several of the leaves of 
cauliflower growing in the field which 
were inoculated on June 18, 1921, were 
dead six days later. Also the curds of 
these plants had large brownrot lesions 
at that time. 
INFLUENCE OF TEMPERATURE ON SPORE 
GERMINATION AND MYCELIAL GROWTH 
It has been pointed out that brown¬ 
rot causes considerable damage to 
cauliflower while in transit. Cauli¬ 
flower reported to be free from disease 
when placed in the car for shipment has 
often been found badly spotted on 
reaching its destination. The question 
naturally arises whether or not the 
fungus can develop at temperatures 
existing in the refrigerator cars in 
which cauliflowers are shipped. In 
order to determine this point, the effect 
of temperature on the rate of germina¬ 
tion of the spores and the subsequent 
growth of the mycelium was studied. 
The method used was essentially the 
same as that described by Weimer and 
Harter (18 ). Preliminary tests showed 
that the spores germinated better in 
sweet-potato decoction (500 gm. sweet 
potatoes per liter) than in either tap or 
distilled water. Hence this medium 
was used. 
EXPLANATORY LEGEND FOR PLATE 3 
A. —Healthy head of cauliflower held as control 
B. —Cauliflower head showing small brownrot lesions resulting from inoculation by spraying with a suspen¬ 
sion of A. brassicae spores from a pure culture. Photographed 5 days after inoculation. Natural size 
C. —Same cauliflower head photographed 13 days after inoculation. Natural size 
D. —Cauliflower head showing natural infection with A. brassicae. Lesions appear as black spots 
