434 
chamber. After 48 hours the inocu¬ 
lated spots were removed, fixed, de¬ 
hydrated, infiltrated with paraffin, and 
sectioned. No evidence of direct pene¬ 
tration of the cell wall was seen. The 
cells showed a change in their reaction 
to stains very soon after the germ 
tubes had entered the stomata of the 
leaf. The cells soon died and the 
tissues affected turned dark. The 
extent to which the fungus spreads in 
the leaf varies greatly. It may form 
only a small dark spot about a milli¬ 
meter in diameter, or it may spread 
throughout and kill a large area of the 
leaf. 
physiology 
Chemical analyses (5) have shown 
that cauliflower contains the following 
carbohydrates: Cellulose, glucose, fruc¬ 
tose, pentosans, and methyl pentosans. 
Dochnowski and Tollens (5) could not 
detect the presence of cane sugar but 
noted the existence of some hydrolyz¬ 
able carbohydrates. On the other 
hand, Busolt (2) was unable to demon¬ 
strate the presence of glucose in cauli¬ 
flower tissue but found mannit instead. 
Experiments were conducted to learn 
something of the carbohydrates which 
may serve as a source of carbon for A. 
brassicae. The carbohydrates tested 
were 5 and 10 per cent glucose, 1 per 
cent Irish potato starch, 5 per cent 
cane sugar, 5 per cent gum arabic and 
cellulose (dissolved and reprecipitated 
according to the method described by 
Scales (15)). Twelve 100 cc. Erlen- 
meyer flasks each containing 30 cc. of 
a modified Czapek’s solution with the 
above carbohydrates substituted as a 
source of carbon were prepared and 
inoculated with a loop of a suspension 
of spores in sterile distilled water. The 
Czapek's solution was modified by the 
substitution of ammonium nitrate for 
sodium nitrate, as was found advan¬ 
tageous for the growth of Rhizopus by 
Weimer and Harter (17). One set of 
flasks had no carbohydrate present in 
order to determine if the fungus would 
grow on this solution without a car¬ 
bohydrate being added. Ten of the 12 
flasks of each set were inoculated and 
the two remaining held as controls. 
The flasks were held at about 30° in 
the dark for two weeks, after which 
observations were made on the amount 
and character of mycelial growth 
formed. There was not a sufficient 
amount of growth made in any of the 
flasks for dry-weight determinations. 
The presence of substances which did 
not go completely into solution, cellu¬ 
lose, starch, and gum arabic in partic¬ 
ular made it impracticable to separate 
the mycelium from the medium by 
Vol. XXIX, No. 9 
filtration; hence attempts to obtain the 
dry weight of the mycelium formed in 
each case for purposes of comparison 
were abandoned. Careful observations 
were made, however, which showed 
that practically no growth took place 
where carbon was not supplied. Glu¬ 
cose and cane sugar proved to be the 
best sources of carbon tried, followed 
closely by starch. Judging from the 
growth made, gum arabic can also 
serve as a source of carbon, but not 
nearly so effectively as the three sub¬ 
stances mentioned above. 
No more growth was made on the 
cellulose medium than in the controls 
where no carbon was present, which 
indicates that cellulose in this form 
can not be utilized by the fungus. In 
order to learn whether this fungus can 
hydrolize the starch and cane sugar, 
samples of the control solutions as well 
as those on which the fungus had 
grown were tested with Fehling’s solu¬ 
tion for the presence of reducing sugars. 
These tests were only comparative. 
Equal amounts of the culture media 
and of Fehling’s solution (20 cc.) were 
used and the solutions were boiled 
approximately the same length of time 
in each case. The control cane-sugar 
solution showed only a trace of reduc¬ 
tion, while some of the same solution 
on which the fungus had grown gave 
a heavy precipitate with Fehling’s 
solution, there being more than enough 
reducing sugar present to reduce all of 
the copper. This indicates that the 
fungus produces a very active invertase. 
Similar tests with the solutions contain¬ 
ing starch showed that there was no 
reducing sugar present in the control 
and only a very little in the inoculated 
solutions. Seemingly, the amylase pro¬ 
duced, if any, was not sufficient to 
hydrolyze the starch much in excess 
of the needs of the fungus. 
Since this fungus produces a rot of 
the cauliflower curd it is of interest 
to know whether an enzym capable of 
dissolving the middle lamellae is pro¬ 
duced under artificial culture condi¬ 
tions. In order to determine this 
point, about 25 cc. of each of the above- 
mentioned solutions were placed in 
small flasks and small pieces of cauli¬ 
flower curd and leaf and sweet potato 
were added. The sweet potato added 
was in the form of circular disks about 
1 cm. in diameter by 0.5 mm. thick, 
cut from the fleshy root. The flasks 
were held at 45°. Five cc. of toluol 
were added to each flask as an anti¬ 
septic. Observations were made from 
time to time but no signs of macera¬ 
tion were evident in any case in 72 
hours. 
Journal of Agricultural Research 
