922 The American Naturalist. [November, 
(2) Natural Methods of Infection —Little that is definite can be 
gathered from Dr. Wakker’s writings. The sticky slime which 
oozes from rifts in the affected leaves is highly infectious, 
adheres to whatever it touches, retains its vitality for some 
time, and is readily borne about on light objects. He discusses 
the possibility of the germs entering through the blossoms, and 
considers that wounds are more likely sources of infection, be- 
cause the attacked blossoms would fall off quickly and carry 
the germs with them. It probably enters the plant through 
wounds made by man or animals. Dr. Wakker thinks it espe- 
cially likely to enter through wounds of the scape made in 
cutting the flower, or through injuries done to the young scales 
by pulling leaves, or by cutting healthy bulbs with infected ° 
knives in process of making incisions in the bulb, or of sepa- 
rating the scales for purposes of reproduction. It is evident, 
however, from the fact that the greater number of the plants 
are first attacked at the tip of the leaf, that some other unknown 
method of infection is the more common one. Dr. W. thinks 
the infection often takes place very early in the spring and 
generally through the air, the sticky bacterial exudate from the 
leaves, etc., being carried to sound plants by wind and rain, or 
by flies and other insects which frequent the hyacinth fields on 
warm days (Verslag, 1883). For various reasons Dr. Wakker 
thinks that the parasite may sometimes enter through the un- 
injured leaf, i. e., through the stomata, but does not appear to 
have induced the disease in this way. Wounds are always 
moist, and the bacterium finds food ready for its use in the 
dead cells of the wound, whereas if it enters through the stom- 
ata it must make its own food from the start. The stomata 
are also very small, and infection through the uninjured leaf 
surface is probably uncommon. 
(8) Conditions Favoring the Spread of the Disease—Dr. Wakker 
states that the spread of the disease is favored by wet weather, 
and that dry weather and continuous sunshine are the best 
preventives. If the much lessened prevalence of the disease 
in 1883 as compared with 1882 is to be attributed in part to 
the precautionary measures taken, it is not less certain that 
the frequent rains of 1882 did great injury to the plants in this 
