5»8 
Journal of Agricultural Research 
Vol. XXVI, No. xa 
rium mother cell at b , and seems to be functioning. There is a rich 
supply of cytoplasm about its base and at c, but little more than would 
be there if the fungus were in a congenial host. In other parts of this 
same infection, however, the mesophyll cells attacked are dead or dying. 
As was mentioned earlier, the first haustorium made by the young 
fungus may be formed in either the epidermal cell or the mesophyll cell 
with which the haustorium mother cell lies in contact. When, as happens 
occasionally, it forms in the epidermal cell, it may attain to full size and 
function for several days. This is a decided advantage to the fungus at 
this critical stage in its life, as it obtains nourishment enabling it to form 
a considerable mycelium. Plate 6, A, illustrates this. The section is cut 
obliquely, showing the two guard cells, a, in perspective, with the empty 
appressorium b fitted into the hollow between them. At c is an oblique 
section through the accessory cell of the stoma. The first haustorium 
in the epidermal cell at d was bisected in sectioning, the other half of it 
being found in the next section. This material was fixed seven days after 
inoculation, so this haustorium is several days old, but it is still living and 
has caused very little disturbance in the host cell. Perhaps because of 
this aid the fungus has formed a fairly rich mycelium which extends 
through several sections. Nearly two dozen mesophyll cells have been 
entered by haustoria, and all are dead or dying. Two of these, at e 
and /, are included in the drawing. In / the engulfed haustorium forms 
a dark-stained body, and a large part of the contents of the cell is con¬ 
tracting around it. A few sections farther on there is a second hausto¬ 
rium in an epidermal cell (PI. 6, B, a). This and the first haustorium are 
the only living haustoria in that entire mycelium. 
It is not obvious at first sight why haustoria of the same individual 
should thrive longer in epidermal cells than in the mesophyll cells ad¬ 
joining them. Epidermal cells have no plastids, and perhaps they differ 
chemically in other respects from mesophyll tissue, and either do not 
possess the power to produce the substance that kills haustoria or possess 
it ill lesser degree. Or, it may be that a haustorium escapes longer in 
an epidermal cell for the simple reason that the latter can not readily 
mobilize its forces. The epidermal cell is very large and possesses the 
minimum of living material spread out as a thin layer lining the long 
walls. It would take time for the living matter of such a cell to flow to 
the point of invasion and surround the haustorium. 
An interesting mesophyll cell was seen in which a haustorium formed 
and grew to a considerable size but was finally killed. A later haustorium 
formed in the same cell and met almost no opposition. It looked normal 
and was covered by only a thin layer of host cytoplasm. The cell per¬ 
haps was too nearly exhausted by the first attack to resist a second one 
effectively. 
In course of time, however, even an epidermal cell can kill a haustorium. 
There are signs of this in one already mentioned (PI. 6, B), for the haus¬ 
torium a, though still living, is covered by a fairly thick orange-stained 
layer and the nucleus b of the epidermal cell is near at hand. In older 
material (PI. 5, D, fixed 11 days after inoculation) the haustorium in the 
epidermal cell at c is incased in a thick layer which is colorless and faintly 
stratified. The haustorium (red-stained) is dead and also shows irregular 
stratification. 1 
Only a few of the hyphse in infections a week or more old show stainable 
contents, and these chiefly at the growing tips. Even the latter are 
relatively scant in content and starved in appearance. The fungus can 
