574 
Journal of Agricultural Research 
Vol. XXVI, No. 12 
Entrance Phenomena 
One or two points, however, should be noted. The urediniospores of 
form III germinate readily and appressoria are formed on the stomata. 
Usually the fungus passes between the guard cells promptly. In some 
cases the entry is delayed, and in others the fungus fails to enter. Ap¬ 
pearances are normal for the first three days. On the fourth day, how¬ 
ever, several cases have been observed in which the guard cells of the 
occupied stoma show slight signs of deterioration. This reaction is not 
general, at least half of the stomata visited by fungi remaining unaffected, 
but when it does occur, it is equally likely to happen whether the fungus 
has entered or not. 
Normally the heavily thickened wall of a guard cell has a strong affinity 
for both the safranin and the gentian of the triple stain. In fact, the 
purple-stained wall is so nearly opaque that it is sometimes difficult to see 
the cell contents. At this stage, in a few cases, the part of the guard cell 
wall in immediate contact with the fungus has undergone some chemical 
change. It no longer takes any stain, but is transparent and glistens con¬ 
spicuously. At first only a small area under the center of the appressorium 
shows this change; later the whole surface in contact with the fungus is 
colorless, and still later a part of the inner wall opposite the appressorium 
is affected. 
Plate i, A, represents a longitudinal section of a stoma showing one of 
the two guard cells with the appressorium a on its outer surface. The 
plant was grown and inoculated in August, 1922, and fixed seven days after 
inoculation. The appressorium is pale and dying and its nuclei are no 
longer distinguishable, for appressoria wither quickly at summer tempera¬ 
tures. The guard-cell wall in contact with the appressorium has lost 
power to stain and part of the inner wall c is pale. The contents of this 
part of the cell also are affected. The guard-cell nucleus has normally the 
form of an elongated dumb-bell. Here the thin connecting strand of 
nuclear material has been dissolved at b. The two ends of the cell are 
still living. In a few cases the reaction is even more pronounced and 
the entire cell is dead. 
A question arose as to whether weather conditions could affect this 
reaction. Three lots of seedlings grown in October, 1921, and in March and 
August, 1922, and fixed six or seven days after inoculation, were studied 
and compared. The stomata of the three lots of material proved to be 
very similar, showing little or no effect of the varying light, temperature, 
and moisture at different times of the year. Of the 68 cases recorded, 
36 showed no change due to the fungus, 28 were more or less harmed, 
and only 4 were completely killed. 
Apart from this reaction on the guard cells, the host and fungus seem to 
be congenial. The fungi which enter develop vigorously. 
Development of the Fungus After Entrance 
The period between the entry of the fungus and the sixth day after 
inoculation is one of intensive vegetative development in the green 
tissue of the leaf. This spongy mesophyll tissue is composed of large 
irregular much lobed cells. Beneath each stoma is a large intercellular 
space, the substomatal chamber, and this is in communication with 
numerous smaller air spaces all through the tissue. More than half of 
the volume of this tissue is in the intercellular spaces. Hyphae with 
rich cytoplasm and large nuclei follow the surfaces of the mesophyll 
