348 
Journal of Agricultural Research 
Vol. XXIV, No. 4 
often happened, would seem to fit none of the groups. These refractory 
cultures caused considerable trouble, and some of them have not yet 
been identified. 
MICROSCOPIC STUOms 
USE OP PHOTOMICROGRAPHS 
The microscopic studies that are most extensively used in classifying 
Fusaria are the size, shape, and septation of the spores. In view of 
the fact that different kinds of spores are produced and that in each 
kind there is much individual variation, the problem becomes in some 
cases rather complex. 
In a goodly portion of the microscopic studies photomicrographs were 
used. The spores were mounted in water containing a small quantity 
of dilute Myer’s flagella stain. The cover glass was blotted with a 
coairse filtered paper, pressed down, and sealed with paraffin to prevent 
evaporation and consequent movement of the spores. The pictures 
were taken soon after the slides were made, for tie mounts gradually 
dried out. If they were put into a moist chamber they could some¬ 
times be kept intact for 24 hours or more. 
The Leitz horizontal photomicrographic apparatus lA No. 398, 
with Leitz microscope stand, having an apochromatic condenser, was 
used for this work. All pictures were taken magnified 500 diameters. 
The photographic method proved very convenient, for by means of 
it actual reproductions of spore material were made when the spores 
were at their best and the data were studied when convenient. This 
permitted a massing of data by means of which close comparative studies 
of microscopic characters could be made, which without photographs 
could not have been done. 
Drawings, of course, might have been used instead, but there is no 
doubt that the photographic method is far superior to that of drawing. 
In the first place, actual reproductions of selected fields of spores are 
made instead of a few spores selected in accord with the personal pref¬ 
erence of the worker and idealized and perfected in the process of 
drawing. Drawings are often misleading in their fine definitions and 
detail. Secondly, if the worker is careful to photograph an average 
field, which in most cases is easy to do, a great deal of additional data 
are recorded on the picture, which the one who was drawing would have 
to add in notes that take too much time when the critical stage of a 
large group of cultures is demanding his attention. Such data, for in¬ 
stance, are the percentage of spores with a certain number of septa, 
the percentage of macroconidia and microconidia, limits of size of 
different types of spores, etc. 
Two complete sets of pictures were taken, except for cultures that 
would not fruit. One was of the fungi from cultures about 47 days 
old, grown on oat agar, and the other of fungi grown on lima bean agar 
when the cultures were about 10 days old. 
The spores of some cultures would not take the stain; others, par¬ 
ticularly those having mostly microconidia, even though perfectly 
sealed exhibited Brownian movement, and still other cultures produced 
so few spores that a field suitable to photograph was impossible to find. 
Many attempts, some of which were successful, were made to grow these 
refractory cultures on a medium that would produce a greater abund¬ 
ance of spores, and whenever successful pictures were taken. Notable 
