23B 
Journal of Agricultural Research 
Vol. vm. No. » 
MACROSCOPIC GROWTH ON VARIOUS MEDIA 
The media used in making these comparisons were Thaxter’s hard 
potato agar, oat agar, Uma-bean agar, string-bean pods, and corn-meal 
agar. 1 Various synthetic media were also used; but owing to the small 
amount of growth produced, they were unsuitable for this work. 
Five different series, consisting of three cultures each of the various 
forms, were made in test tubes and grown at room temperatures. Owing 
to differences in the hardness of the media, amount of moisture, air, etc., 
there were slight differences in the amount of aerial mycelium in the 
different series; but in general the results in all were practically identical 
and uniform. 
As a minor character, the appearance of the macroscopic growth on a 
given media is of some value when taken with other distinguishing 
characters. Plantings of the different forms on potato agar poured in 
large petri dishes, which offer more uniform conditions than can be ob¬ 
tained in test tubes, also showed differences in the luxuriance of growth 
in some of the species. The distinguishing characters, however, are best 
shown when grown in test-tube slants. Potato agar was found to be 
best suited for this purpose. A summary of results of the growth on 
this medium 12 to 18 days after the transfers were made showed that 
the cultures may be divided into three groups, as follows: (1) Growth 
very profuse, aerial, and fluffy. In this group are included P. para¬ 
sitica, P. fagi, P, jatrophae, P. cactorum, and P. faberi. (2) Growth less 
profuse, more or less embedded in substratum, lacking the fluffy appear¬ 
ance, irregular surface, often forming numerous pellicular-like growths 
and presenting a granular appearance. In this group are included P. 
syringae and P. nicotianae. (3) Very little or no growth. In this 
group are included P. infestans and P. phaseoli. 
On oat agar, unlike the potato agar, P. syringae alone could be dis¬ 
tinguished at all times from the remaining forms. The character of 
growth for this form was similar to that on potato agar. All the other 
forms make a profuse white fluffy growth on the oat agar. 
On bean pods no difference could be detected, all forms making a 
good, fluffy growth except P. infestans and P. phaseoli, which made 
little or no growth. 
On corn-meal agar no difference could be detected between the differ¬ 
ent forms, but all made scantier growth than on the other media. 
On Tima-bean agar all forms, including P. infestans and P. phaseoli, 
made a profuse white growth. 
1 Thaxter's hard potato agar, 200 gm. of potato, 20 gm. glucose, and 15 gm. of agar for every i.ooo c. c. 
of water; Clinton's oat agar, made according to the directions given by Clinton (8), except that rolled oats 
and i% gm. of agar for every 1,000 c. c. of media were used; bean-pod plugs, consisting of pods of ordinary 
string beans placed in test tubes with a small quantity of water and sterilized; corn-meal agar, made accord¬ 
ing to the directions given by Shear and Wood (32); Lima-bean-juice agar, made according to the directions 
given by Dastur (10). 
