26 BULLETIN 727, U. S. DEPARTMENT OF AGRICULTURE. 
Incipient and advanced stages of penetration, as seen in surface 
view, are illustrated in figure 1. The appressoria are seen to be 
quite uniform in size, shape, and size and shape of germ pore. Al- 
though this material was subjected to several hours’ washing in 
running water, the appressoria remained adherent to the cuticle. 
From a study of these preparations it appears that penetration 
never occurs except from an appressorium and that penetration 
occurs directly through the cuticle. From this, it seems safe to con- 
clude that the appressoria have a definite function in connection 
with host penetration. No cases of stomatal entrance were found. 
A case was found in which a spore lying directly over a stomatal 
opening formed an appressorium at one side. 
To better understand the mode of penetration, material similar to 
that above described was fixed in 10 per cent HCl, acetic alcohol, or 
Gilson’s fixative, embedded, sectioned, and stained in the triple 
stain or Haidenhain’s iron alum hematoxylin. Numerous penetra- 
tions were found in sections from fixations made 65 and 121 hours 
Fic, 3.—Cross section of leaf epidermis, showing Fic. 4.—Cross section of the outer wall of a 
penetration of epidermal cell from an appres- leaf epidermal cell, showing an incipient 
sorium, 65 hours after inoculation. The tip of stage of penetration from an appressorium, 
the penetration tubeisswollen. (Camera-lucida 65 hours afterinoculation. (Camera-lucida 
drawing; magnified about 575 times.) drawing; magnified about 1,300 times.) 
after inoculation, and types are ulustrated in figures 3 and 4. The 
latter represents an incipient stage. Here, again, it is seen that 
direct penetration of the cuticle and outer wall takes place. Stomatal 
entry does not occur. In one case (fig. 5) an appressorium has been 
formed in the stomatal pore and penetration of a guard cell has fol- 
lowed, rather than a direct invasion of the substomatal chamber. 
In figure 6, showing an apparent stomatal penetration, close exam- 
ination reveals that the lower guard cell was pierced by the penetra- 
tion tube, which then emerged into the substomatal chamber. 
Appressoria may be distinctly flattened on the side next to the 
cuticle (fig. 6), and all are in very close contact with the latter. The 
penetration tube varies in shape, but is usually more or less club 
shaped, owing to the fact that it becomes swollen after gaining 
access to the lumen of the cell (fig. 3). In figure 7 it is quite evident 
that the contents of the appressorrum have entered the penetration 
tube. In no case has it been possible to trace the course of the 
penetration tube through the cuticle and underlying wall layers. 
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