Apr. a8,1923 Specics of Fiisatium Isolated from Potato Tubers 
347 
from the spore it was considered pure and the culture was kept as a 
stock. If there was any question as to the source of the growth the 
culture was discarded. Sometimes a number of attempts had to be 
made before the stock culture was obtained. 
COMPARATIVE CUWURAL STUDIES 
Since the purpose of our work was the identification of the species of 
Fusarium that we had found occurring on potatoes in Montana, we began 
by comparing the cultural characteristics of each isolation product, 
hoping to be able to group together those which belonged to one species 
so that we might eliminate unnecessary duplication with cultures of the 
same species. This hope was realized only in one group. After a very 
few trials with different media and at different ages, one group, containing 
about 20 per cent of all the cultures, separated itself out very constantly. 
Its growth was so characteristic that we then believed and have since 
proved that it was Fusarium trichothecioides Wr. There were other 
groups, some seven of them, each containing from 2 to lo cultiures; but 
the identity of the members of the groups was not sufficiently striking 
to warrant leaving any of them out of further studies. However, these 
groupings aided materially when actual identification work began. 
Seventeen series of cultures have been studied. A series consisted of all 
the transfers made at the same time and incubated under similar con¬ 
ditions for the purpose of comparative studies. At least four sets of 
individual notes were taken on each series, so as to bring in the influence 
of age on the characters. 
The characters emphasized in these notes were color, amount, and 
nature of the growth of mycelium, absence or presence and color of 
pseudopionnotes or sporodochia. All color determinations were based 
on Ridgway’s “Color Standards.” ® 
In practically all the series the cultures were inoculated in triplicate, 
so that when variations arose between cultures inoculated from the same 
stock culture a decision as to which was the more normal could be made. 
As a preliminary to note taking, those cultures which had sufficient 
similar cultural characters to suggest identity were put into groups. 
Each group was designated by a letter, and these were placed in a table 
in parallel vertical lines, a column for each note taking, so that gross 
group comparisons could easily be made. Notes on each group were made 
in detail at the end of the table. If a culture showed only a slight variance 
from a group it was put into the group, but with special additional notes, 
and was designated in the table by the group letter with a subnumber. 
In so far as possible the same letters were used throughout for the same 
group. After a few sets of notes were taken one or two cultures which 
seemed most typical of a group were chosen as type cultures, and these 
numbers were given the same letter each time and served as the nucleus 
for the group represented by that letter. 
Some few cultures, the number varying with the medium on which 
they were grown, did not develop any distinctive microscopic characters; 
others developed distinctive characters on certain media; and occasionally 
the same culture when on one medium was placed in a certain group, 
while on another medium it would be placed in a different group, or, as 
• Ridgway, Robert, color standards and color NOMBNCLATURe. 43 p., S3 col. pi. Washington, 
D. C. igia. 
