224 BOTANICAL GAZETTE [SEPTEMBER 
in general appearance. There were five larvae in the two together. 
One of these is sketched in the figures as it was fixed and remained in 
the opening of its hole. The larvae were determined by Mr. W. A. 
Riley, of the Department of Entomology of Cornell University, as 
dipterous larvae of family Mycetophilidae. Further identification was 
impossible, and since an attempt to cultivate them resulted in the loss 
of one and the larger part of one gall, the remainder were killed and 
fixed for study. 
To see what changes had occurred in the tissues, portions of one 
gall were imbedded in paraffin and sectioned for comparison with 
Omphalia campanella Batch 
Fic. 5.— Camera lucida sketch of normal hyphae. 
Fic. 6. — Camera lucida sketch of hyphae from the gall. ~ 
sections of a normal Omphalia gathered from the same place. Camera 
lucida sketches of portions of these sections look at first very much 
alike. The intercellular spaces are reduced somewhat and the hyphae 
appear swollen. Measurement of the diameters of a large number of 
hyphae gives a marked contrast. The average of forty measurements 
of diameters of cells in the same microscope field was, in the normal 
tissue, about 7; in the gall the average was between 9 and 1op (figs. 
5, and 6). These figures show the stimulating effect of the attack of 
the gall insect. It has in this case not only produced a relatively very 
large growth, but has caused a very noticeable increase in the average 
size of the hyphae (nearly one-third). Hyphae of normal size occur 
among the swollen threads of the gall, and larger ones are found in the 
normal tissue, but the averages are strikingly different. A stimulus 
which is to produce so marked an effect, both in obliterating the lamel- 
lae completely and increasing the size of the hyphae themselves, must ne 
applied to the mushroom before gill formation has taken place, else its 
effect would be destructive, not constructive. It would seem, then, that 
in these cases the eggs must have been laid very early, so that the abnor- 
