131 
studded with small dewy drops, apparently of precisely the same character 
as the “‘callus.’’ (See Fig. 23, page 135.) 
The host's cell-wall at and near the point of penetration, is markedly 
altered chemically, as is shown by various stain-reactions. Thus, adjacent 
to the point of infection several different regions giving different chem- 
ical reactions may be distinguished, as is indicated in Fig. 19. Region 3 
gives the usual chlor-zinc-iodide reaction and stains like normal cellulose. 
None of the other regions do this. Region 4 stains darker with the usual 
Fic. 19.—H. No. 1: regions of a young diseased spot: 
1, mycelium; 2, penetrating mycelium; 3, normal wheat 
cell-wall; 4, region of darker staining; 5, region of lighter 
staining; 6, diseased inner lamella; 7, middle lamella; 
8, ‘‘callus.”’ 
stains, but not so dark as normal cell-wall. The “‘callus’’ and penetrating 
mycelium stain faintly or not at all. The middle lamella stands out clearly 
in all of the diseased region, and on each side of it the inner lamella is seen 
to be thickened and of altered stain-reaction. Though penetration is some- 
times directly through the wall it is much oftener into the middle lamella, 
and the mycelium shows a strong tendency to follow along the line of 
division between two cells, thus giving a gridiron effect to the mesh. This 
is possibly due to chemotropic attraction by the middle lamella or, possibly, 
because this is the weakest place in the cuticle. No case of stomatal 
entrance was observed; indeed, on the sheaths of “Golden Chaff’ wheat 
stomata are seldom present. 
Once within the host cell the mycelium grows rapidly, soon nearly or 
completely filling it (Tig. 20), and often forming a mass so dense that it 
resembles a pseudoparenchyma. Both longitudinal and transverse sections 
