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that the larva has the power of producing some peculiar 
irritation which causes an overflow of the sap necessary for its 
food.” Furthermore it has been remarked by several observers 
that no traces of excreta are to be found in the closed galls. 
Now it was plain that in my sections the central pith of 
the stalk was absent, but that so far from any other “lesion” 
of the plant being evident, the woody portions of the bundle 
ring as seen in section were increased and thickened. 
The larva seems to fill the cavity, leaving barely room to 
turn in; and no excreta are present. In most sections the body 
of the larva was sliced through and remained in the cavity 
which it just fitted. 'The food must consist of the fluid which 
flows through the bundle, or of broken inner bundle cells 
torn by a movement of the larve within, probably of both. 
The absence of solid excreta is remarkable. I suggest that 
they are fluid and exercise an irritating or other effect on the 
plant cells, probably hardening, or at any rate altering the 
substance of the cell wall. This is partially borne out by the 
fact that a bundle from a gall will not take staining fluids that 
are effective with a normal section, indicating some change of a 
chemical or mechanical kind. 
I hope to show in a subsequent paper the gradual change 
of the tissues, studied from galls of varying ages from the first 
appearance of the swelling on the flower stalk; as well as com- 
parative studies, from other Cecidomyid galls, which are now in 
progress. 
More than 25 years ago a writer on galls expressed his 
opinion that little more was to be discovered regarding them. 
I rather incline to the view that a very wide field for research 
remains still but partially explored. 
