168 
Journal o f Agricultural Research 
Vol. XXIX, No. 4 
inoculated with cultures of various 
fungi that had appeared in isolation 
plates inoculated from corm lesions. 
The inoculations were repeated, as in 
the preceding experiments, but neither 
the old nor the new corms became in¬ 
fected. 
Introducing Bacterium marginatum 
into wounds made in mature corms did 
not produce any rot. This was tried 
three times with different degrees of 
heat and moisture, using varieti s 
known to be susceptible. There wa 
no reaction beyond a slight browning 
and the formation of an imperfect 
layer of cork. These corms were then 
planted and produced normal plants. 
Tests showed the juices of these 
gladiolus corms to be very acid. It is 
possible that the bacteria coming into 
direct contact with large amounts of 
the acid juice from the w T ounded tissues 
were not able to grow. 
Potato tubers were copiously inocu¬ 
lated with this organism but no trace 
of rot resulted. 
MORPHOLOGY 
Obtained directly from the host the 
organism is at first sluggishly motile 
but after a few minutes it becomes 
more active. Staining with carbol 
fuchsin shows rods of varying sizes, 0.8 
to 1.8 by 0.5 to 0.6m. Many are so 
short as to resemble cocci. The rods 
are rounded at the ends and occur 
singly and in pairs. 
From 3-day-old cultures of peptone- 
beef bouillon the rods stained with 
carbol fuchsin measure 0.9 to 1.8 by 
0.5 to 0.6m. Longer rods are found, 
but these usually show division lines. 
The bacteria stain well with all the 
usual stains. Capsules are present on 
bacteria obtained directly from the 
host and are also formed in beef media, 
and in Thaxter’s potato agar (Ribbert’s 
capsule stain was used). No spores 
have been found. The organism is 
motile by means of 1 to 4 bipolar 
flagella. The flagella are mostly found 
at one end only. However, careful 
search shows occasional rods with 
flagella at both ends; a single flagellum 
at one pole and one to two, rarely three 
flagella at the opposite pole. In the 
mounts examined the rods having four 
flagella at one pole have none at the 
opposite pole (PI. 5, I). The flagella 
are 3 to 8m long. These were stained 
by Casares-Gil’s method. Gram-nega¬ 
tive. Not acid fast. Long chains de¬ 
velop in 2 and 3 per cent salt-beef 
bouillons, short chains in the usual beef 
media. Involution forms as very slen¬ 
der granular rods were found in beef 
bouillon cultures grown at 39° C. In 
potato agar plus dextrose the bacteria 
are usually large, some as wide as 0.8m, 
and rather granular. In 1 to 4 per 
cent dextrose water cultures the growth 
s scanty and numerous, myceliumlike 
forms are produced. 
CULTURAL CHARACTERS 5 
Agar poured plates. —On peptone- 
beef agar, reaction+ 10 to+14, colo¬ 
nies appear in 18 to 24 hours and 
under favorable conditions are often 
10 to 12 mm. in diameter at the end 
of 5 days. Colonies are at first circu¬ 
lar, smooth, shining, almost hemis¬ 
pherical, usually amorphous and 
opaque, sometimes thinner, translu¬ 
cent and with concentric striations. 
Margins entire. In 1 to 3 days a 
marginal growth develops, which in¬ 
creases from a thin, narrow, barely 
visible film (PI. 5, A) into a well-defined 
border of considerable width and thick¬ 
ness. Average colonies 4 to 5 days old 
have centers 2 to 3 mm. in diameter, 
surrounded by borders 2 to 4 mm. 
wide. (PI. 5, B, C and G). Well isolated 
colonies sometimes produce borders 7 
to 8 mm. in width (PL 5, D). The 
border, at first extremely and uniformily 
thin, becomes thicker and contoured by 
the development of short, more or less 
irregular, radiating ridges. In 8 to 14 
days the border is about as thick as 
the central area which remains smooth 
and does not increase appreciably in 
diameter (PI. 5, E). The appearance 
and development of this outer margin 
is greatly influenced by the tempera¬ 
ture and the degree of isolation. The 
growth is white, soft, and viscid in 
consistency. Buried colonies are round 
to oval, occasionally triangular, out¬ 
lines smooth, opaque becoming trans¬ 
lucent. In thickly sown plates the 
characteristic marginal growth may be 
so delicate as to escape casual obser¬ 
vation and sometimes it is entirely 
lacking. 
Agar stabs. —In peptone-beef agar 
growth is good on the surface, uni¬ 
formly thick, smooth, white, opaque to 
translucent. The stab is visible for a 
5 Cultures were grown at room temperature, approximately 25° C., unless otherwise specified. 
Beef infusion was used for all the beef media. 
Difco peptone and Eimer and Amend agar were used in the media. 
For the media used for the optimum reaction for growth three sets of determinations were made. 
First, it was titrated and the Fuller scale readings obtained, then Ph determinations were made colori- 
metrically, according to the Clark and Lubs’ method, and electrometrically. 
“Color Standards and Color Nomenclature”: Robert Ridgway.used in describing color in cultures (7). 
