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F. D. FROMME 
of growth by a turn of 90° or 180° and had then grown away from the 
Hght {jig. lb). The incidence of light, therefore, not only had a pro- 
nounced effect in determining the direction of growth of the germ- 
tubes, but also determined to a considerable degree the approximate 
part of the spore wall at which the germ-tube issued, i. e., the part 
farthest from the light. The other pores on the shaded part of the 
spores were likewise stimulated to some degree and a noticeable 
swelling of their gelatinous contents was often apparent. Sometimes 
Fig. 2. Germinating urediniospores of Puccinia Rhamni after an exposure of 
three hours to a unilateral illumination. The arrow indicates the direction from 
which light was admitted. 
two germ-tubes issued from the shaded side but one of them soon 
outgrew the other. When the spores were germinated in darkness the 
tube issued from any one of the pores. 
No theory to account for the presence or significance of more than 
one germ-pore in urediniospores has been advanced. If a possible 
explanation in terms of advantage is permissible, it seems reasonable 
to assume that a germ-tube in nature arising from the shaded side of 
the spore, adjacent to the leaf surface, would be in a more advantageous 
position to effect an entrance into a stoma than one arising from the 
non-shaded side, away from the leaf. A urediniospore with several 
pores should, therefore, have a better chance of producing an infection 
than one with a single pore. 
The importance of these light reactions of germinating uredinio- 
spores from a pathological viewpoint may be found in the possible 
explanation of certain phases of infection that they suggest. The 
