56 Journal of Agricultural Research voi.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 wa3^ 

 Camera-lucida 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 

 handUng, 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- 



