138 BOTANICAL GAZETTE [AUGUST 
organs are so firmly fixed to the slide that they are not easily washed 
off by a jet of water. Other spores remain floating in the drops of 
water, being held by the surface film. These also germinate readily, 
but they never form adhesion discs while the germ tubes remain 
free in the water. Other spores were sown in drops of water 
placed on the surface of apples. These behaved in the same way 
as those on slides. Spores in hanging drops produced mostly mycelia, 
since very few germ tubes came into contact with the glass. The 
experiment was then varied by substituting beet infusion for the 
drops of water. The result was striking. The germ tubes pro 
duced no appressoria, but grew out into long hyphae, regardless 
of the fact that they were often in contact with the surface of the 
glass or with the cuticle of the apple. When sown in nutrient media 
of any kind, solid or liquid, the spores of Gloeosporium germinate 
and form mycelia directly. 
These experiments show that the formation of appressoria |S 
induced by a contact stimulus, but in the presence of abundant 
nutrient material the germ tube loses its power to react to contact 
stimuli, and the formation of appressoria is inhibited. If this were 
not the case, the mycelium would react to the contact of evéty 
obstacle, such as cell walls or starch grains, which it met in its course 
through the tissues, and growth would thus be made practically 
impossible. This is illustrated by the behavior of spores in weak 
beet infusion. Here the germ tube shows a tendency to form esi 
appressorium, but before this is well formed it grows out again 
into a mycelial hypha, which immediately repeats the process. In 
old agar cultures which have been exhausted, the hyphae form 4 
series of thick-walled cells of the nature of appressoria. These do 
not have the normal shape, but assume fantastically lobed forms, 5° 
closely crowded that they resemble sclerotia-like masses. The 
exhaustion of the nutrient material in the agar and the contact 
with the glass or other solid particles no doubt leads to the formation 
of these masses. ; 
GERMINATION OF THE APPRESSORIA. 
: A : : ith 
The appressoria germinate readily on a slide when covered ee 
nutrient solution. The germ tube always emerges from the pe 
