254 
Journal of Agricultural Research 
Vol. I, No. 3 
It will be seen, therefore, that the following characteristics belonging 
to the dry-rot fungus are not found in the foot-rot organism: (i) Stroma; 
(2) chambering of the pycnidium; (3) conidiophores conspicuously long 
and awl-shaped; and (4) long, filiform, hook-shaped stylospores. 
What is believed to be even more significant than the differences in 
morphological characters between these two organisms is the difference 
in parasitic habits and growth in artificial cultures. It has been pointed 
out in a previous bulletin 1 that the dry-rot fungus does not kill the 
plant but lives in apparent harmony with it without injury. The 
pycnidia appear on the stem only after the plant has been lifted and 
kept in a damp chamber for- 10 days or 2 weeks, this being the first 
evidence that the plant was infected. The organism occurs on the 
petioles and leaves of dead plants and often develops on apparently 
sound roots after a period of time in storage. Stylospores are frequently 
found on the roots and stems. 
The foot-rot disease, on the other hand, kills the plant in three to 
eight weeks after infection by the destruction of the cortex of the stem 
for several inches above and a little distance below the surface of the 
soil. Pycnidia are formed on the diseased portion of the stem about 
the time the foliage begins to wilt (PI. XXVI, fig. A)> and under field 
conditions even earlier. 
The growth of the organism on several kinds of the commonly used 
artificial media and especially on synthetic agar 2 and on com meal 3 * 5 fur¬ 
nishes additional means of distinguishing the two diseases. 
On synthetic agar the foot-rot fungus grows slowly and under normal 
conditions forms a very compact growth, at first irregular in outline with 
a slightly darker center, attaining a diameter of not more than 2 or 3 mm. 
at the end of a week or 10 days. (PI. XXVII, fig. B .) On the same 
culture medium the dry-rot fungus grows much faster, forming a loose, 
flaky growth of uniformly white hyphae having an irregular outline. 
(See PI. XXVII, fig. A .) The growth of the dry-rot fungus is so loose 
and inconspicuous that it is scarcely visible until it has attained a diam¬ 
eter of 2 or 3 mm. 
1 Harter, I,. L., and Field, Ethel C. A dry rot of sweet potatoes caused by Diaporthe batatatis. U. S. 
Dept, of Agr., Bur. Plant Indus., Bui. 281,38 p.,4 pi., 1913. 
2 Synthetic agar is prepared as follows: 
Distilled water. 
Dextrose. 
Peptone (Witte's). 
Ammonium nitrate. 
Potassium nitrate. 
Magnesium sulphate. 
Calcium chlorid. 
Agar agar. 
Grams. 
1,000 
200 
10 
10 
5 
2-5 
o. I 
20 
Place the water in the beaker first; then add other ingredients in the order given. Stir and let stand 
till the agar agar is moist. Steam 1 hour. Tube with constant stirring. Plug and autoclave for 15 minutes 
at no 0 C. Agar of high purity only should be used. 
5 Corn-meal flasks are prepared as follows: Place 5 grams of com meal in a 100 c. c. flask. Add 45 c. c. of 
distilled water and steam for 15 minutes. Plug and autoclave at 11 pounds pressure for 20 minutes. 
