Jan. 20, 1923 
Cytological Study of Injection 
135 
of a stoma with its long femur-shaped guard cell containing plastids and 
the elongated dumb-bell-shaped nucleus, and a slant section through the 
adjoining accessory cell. At this stoma is a fully formed appressorium 
a with a withered remnant of germ tube still attached. Plate 3, D, 
shows a surface view of an appressorium on Kanred at the same stage. 
The two guard cells are flanked by accessory cells, and the appressorium 
is fitted closely into the hollow above the stomatal slit. 
In spots where the spores were crowded on the leaf, slides were 
obtained showing several germ tubes competing for the same stoma. 
Plate 1, B, shows a longitudinal section of a stoma with three appressoria. 
The fixing fluid used for this preparation was a modification of Bouin’s. 
The fluid proved to be too strong, but it is interesting to note that while 
the guard cell of the host shows pronounced plasmolysis, the fungi them¬ 
selves are well fixed. This is perhaps an indication that the fungus has 
considerably higher osmotic pressure than its host. In this figure 
appressorium a evidently arrived first at the stoma, as it occupies 
nearly the whole hollow. Appressorium b came second and filled in one 
end of the hollow. It is evidently younger, being smaller and binucleate. 
Appressorium c is just entering, and its germ tube is forming a swollen 
club-shaped mass on top of a. The three germ tubes leading into these 
appressoria leave no question as to the separate origin of these three 
contestants for the place. 
In nearly all cases the formation of the appressoria takes place with 
great regularity. A few deviations have been observed. Each of the 
little ridges running lengthwise of the surface of the leaf is reinforced at 
its apex by a slender band of heavy-walled lignified cells, studded at 
regular intervals by stout little thorn-shaped hair cells. In two of 
three cases an appressorium has been found wedged into the angle 
between the base of the hair cell and the adjoining epidermal cell. 
Plate 1, C, at a represents a cross section of one of these. The adjoining 
epidermal cell b is dead and collapsed. In another case (PI. 1, D), taken 
from a longitudinal section of a leaf of Mindum, an appressorium formed 
on a dead collapsed ridge cell, failed to enter, pushed out a tube and 
grew to the other end of the host cell, and made a secondary appres¬ 
sorium there. Perhaps the dead host cell in each case allowed the 
diffusion outward of materials or of water from within the host, which 
served to attract the fungus. No appressorium has yet been observed 
on an ordinary healthy epidermal cell. These irregular cases form an 
argument against Fromme’s theory (15) that ‘ ‘negative heliotropic reac¬ 
tions play an important part in bringing about the stomatal entrance 
of the germ-tube.” 
In entering the host plant the appressorium pushes a bladelike wedge 
through the stomatal slit, and the contents of the appressorium flow 
through, commonly forming a swelling inside which is termed the “sub- 
stomatal vesicle.” 
Plate 1, E, shows across section of a stoma and the substomatal chamber. 
The stoma is occupied by the entering fungus. The collapsed germ tube 
and the appressorium can be seen outside the stoma and the beginning of 
the vesicle inside. 
Plate 1, F, a longitudinal section of a Mindum stoma, represents a more 
advanced stage fixed on the second day after inoculation. It is drawn 
on a smaller scale than the preceding. The living content of the appres¬ 
sorium has passed through the stoma, leaving the delicate wall of the 
appressorium with its withered germ tube empty and wrinkled but not 
