Ar ie nnn ee oe Pere De 
Mee sedteats aN WRC EN BENCH Ne SUeeN oat te hes ie 
. SECTION OF VEGETABLE PATHOLOGY. — - 383 | 
hs, bas that it is seen with difficulty, but when older the walls of the | 
_ filaments are thick and have a double contour, as of a tube within 
a tube, and the protoplasm is to be seen in the middle (Figs. 2 a, and 
8). The color is a peculiar glistening opalescent or bluish-white; but 
the threads are often enveloped by a coating of cellulose and ob- 
secured by it so as not to be easily detected. It is difficult to trace the 
fungus from the place of entrance to that of spore formation because 
the intermediate mycelium dies out or is absorbed. me 
The fruiting time of the corn is also that of the fungus; and its 
spores are most commonly formed upon the young kernels or contig- 
uous parts. 
(d) SPORE FORMATION. 
(Plate XII, Figs. 15-17, and Plate XIV, Figs. 5-12.) 
The first step toward spore formation is the branching of the 
mycelial threads in the place where spores are to be formed. The 
spore-forming threads branch ina bush-like manner, andthe branches 
formed are very slender. These, in their turn, branch repeatedly; 
at length a very complicated mass of branches is formed. This in- 
crease in the fungus causes the swelling of the plant, and the ma- 
_. turing of the spores completes the swelling. The latter consists, in 
addition to the mass of fungus threads, of an abnormal multiplica- 
tion of the tissues of the host plant. The tips of the branching 
threads become swollen and distended with protoplasm and have a 
color and appearance similar to that of the mycelium; in this pro- 
toplasm granules 5 an each of which is to become a spore (Plate> 
XVI, Figs. 9-11). These gradually increase in size and the filament 
becomes considerably distended, so as to resemble a short string or 
cluster of beads. _ 
The developmentis now very active, and lateral protrusions or short 
- branches are frequently formed. Soon cell walls are formed across - 
the filaments, one between every two of the nuclear formations. 
The distending results in a roundish cell for each of these. The 
cell walls become gelatinous, which gives the slimy character to the 
mass of smut. As the spores approach maturity the gelatinous 
walls are gradually absorbed, as are also the mycelial threads, so. 
that at maturity very little remains but the dry, dusty spores. Those 
in the center of the mass mature later than those outside, and when ~ 
the latter are dry the former may be found still slimy. 
The spores (Plate XIII, Fig. 17) are globose or roundish-oblong in 
form, and the central mass of protoplasm is inclosed by a double 
- wall, the inner colorless, the outer brownish-black and thickly cov- 
ered with slender points. This outer wall is similar to that of pollen 
grains. ‘Their size is from .00036 inch to .00048 inch (92 to 12y), or 
about 25,000 laid side by side would measure an inch. 
(€) GERMINATION. 
Vitality of spores and time of germination.—Kiihn states that the 
spores germinate with difficulty or not at all in water, but that in a 
moist atmosphere they germinate readily in October, and reach the 
_ formation of conidia in twenty-four hours. Fischer de Waldheim 
obtained similar results. Brefeld also failed to germinate the spores 
in weter in the fall. He found, however, that in the spring ger- 
