tort] ; COOK—PROBLEMS IN CECIDOLOGY 389 
James Pacet, as late as 1880, said that “‘the most reasonable, 
if not the only reasonable theory, is that each insect infects or 
inoculates the leaf or other structure of the chosen plant with a 
poison peculiar to itself.” Unfortunately, this view is still held 
by most of our biologists, although the researches of the past thirty 
years have demonstrated that it is almost without foundation. 
In 1881 Dr. HERMAN ADLER? published the results of his long 
and careful studies, in which he gave the first real scientific evi- 
dence concerning the nature of the stimuli and character of gall 
formation. According to his results, the fluid secreted by the oak- 
gall fly is not irritating, and is not a factor in gall formation, but 
May serve as an antiseptic dressing for the wound in the plant. 
This view is strengthened by BEYERINCK,' who demonstrated that 
the fluid is without taste or smell and not irritating when injected 
under the skin. ApLER advanced the idea, which has been affirmed 
by other workers, that in the oak-gall flies, whatever irritating 
chemical exists comes from the larva and not from the parent insect. 
ADLER also reports his observation on Nematus Vallismierii, one 
of the saw flies, which attacks the Salix amygdalina. In this 
case the female pours out an abundant glandular secretion at time 
of oviposition, and the gall is well formed before the larva emerges 
from the egg. 
It is also well known that mechanical stimuli will frequently 
Cause abnormal growths. However, accurate data upon the results 
of various stimuli is not to be found in our literature. 
ADLER says that the cecidia always originate from the formative 
cells of the plant, and that if the stimulation is applied to any other 
than the formative cells, cecidia are not produced. This statement 
Opens up an enormous line of work. While some scale insects cause 
hypertrophies, others do not. Who has traced the ramifications 
of the mouth parts of these insects through the tissues of the host ? 
Why do some Uredineae cause cecidia while other closely related 
Species do not? Who has traced the mycelia of these related species 
’ Ueber den Generationswechsel der Eichengallen. sais Wiss. Zool. 35: 
T5I-246. 1881. Translated in 1894 by CHARLES R. STRA 
‘ Beobachtungen iiber die ersten seca cl chain einiger Cynipidengallen. 
Naturk. Verli. der Kon. Akad. Deel 22: 179. 1882. 
