56 
Journal of Agricultural Research 
Vol.V, No. i 
seedlings from the control pots were killed in Flemming's solution, embed¬ 
ded, sectioned, and stained with the triple combination in the usual way. 
Camera-ludda drawings from the slides thus prepared are employed to 
illustrate this discussion. Most of the seedlings were still in the cotyledon 
stage, but some that had recovered from the attack had developed their 
first pairs of leaves. Seedlings which had been entirely killed were so 
badly disintegrated or so softened by the disease that they did not yield 
satisfactory material for study. The sections showed the cells in a con¬ 
dition of complete collapse and decay. The cellulose layers of the walls, 
as well as the middle lamella, were gelatinized and softened to such an 
extent as to have lost most of their rigidity. The walls were broken 
and fragmented, but this may have resulted from handling during the 
process of washing and dehydrating. Bacteria were present, of course, 
and the softening of the walls, which made them so liable to fracture in 
handling, may have been due in part to the action of these agents. 
Cells of badly diseased but still living seedlings presented more favor¬ 
able material for studying the histological relations of the parasite and 
host. The cells were often nearly filled with the fungus, which showed a 
tendency to remain within the cell rather than in the middle lamella, 
although it frequently penetrated the walls (PI. I, fig. i). Now and 
then a thread of the fungus was observed running between the cells 
for a little distance, but the indications are that, while the organism 
dissolves the middle lamella, it does not feed upon it. Heavily invaded 
cells are consumed, the cytoplasm disappears, and the nuclei disintegrate. 
The middle lamella gelatinizes, so that the cellulose lamellae may become 
widely separated while the cellulose layers are broken and disintegrated 
or even dissolved (PI. I, fig. 2). The first visible indication of the 
alteration in the walls is a change in their reaction toward the stain. 
They take the safranine more deeply and retain it more tenaciously than 
do the walls of normal cells. With the progress of the disease a border 
area of increasing width, which also takes the safranine deeply, develops 
on either side of the walls, as if the substances which retained the dye 
were gradually diffusing from the wall and spreading into the surrounding 
space. 
In cases of less serious infection, where recovery is possible, or in tissues 
which have just been invaded, a somewhat different condition exists. 
Plate I, figure 3, represents a recently invaded portion of a rather 
badly diseased seedling which would probably have been unable to 
recover. The cell walls show the gelatinized condition only in a moderate 
degree and in an area confined to the points where it has been penetrated 
by the mycelium. The mycelium has expanded in one of the cells in a 
manner not frequently noted, and the effect of the parasitism is apparent 
in the abnormal condition of the host nuclei. Evidence of disease was 
sometimes manifested in the neighboring uninfected cells of such mate- 
