DEVELOPMENT OF PHYLLOXERA VASTATRIX LEAF GALL 35 1 
galls, in which the stimulus is applied in one direction only, and also 
exists in the highly complex Neuroterus gall described by Weidel (31). 
This latter author believes that mechanical stimuli are the factors in 
the production of even the most highly developed Hymenopterous 
galls. He questions Beyerinck's (i) hypothesis of chemical stimula- 
tion and asks why is it that the proliferation is more pronounced 
around the larva, i. e., in tissues some distance away, than in tissues 
immediately in contact with it? Cosens, who believes that gall pro- 
ducers secrete enzymes which bring about cecidial formation, answers 
this question by saying that it seems likely that the enzyme content 
requires a certain degree of concentration in order to exhibit its maxi- 
mum activity, and that immediately in contact with the larvae the 
enzymes do not possess the requisite degree of dilution to cause the 
greatest stimulation. 
In the Phylloxera galls, as noted, the tissue next to the nymph 
shows no increase in the number of cells, and furthermore the tissue 
immediately around the proboscis showed no proliferation. If this 
insect introduces any diastatic enzymes, as Cosens believes, they must 
be introduced as salivary secretions by means of the proboscis, since 
secretions from such structures as cenocytes, as Rossig (25) describes, 
or Malphigian tubules, as Triggerson (28) describes, of the insect 
body, would be made in this case on exposed leaf surfaces with very 
little chance of entering the leaf. I have sprayed solutions of diastases 
on young vine leaves and observed no indication that it entered the 
leaf. According to Cosens's hypothesis the area immediately around 
the proboscis would not grow much, because the concentration of the 
enzymes would be too great, but further away, where the concentra- 
tion of the enzymes would be less, growth would be greater. It is 
difficult on this basis to explain the phenomena under consideration. 
Cosens assumes that these enzymes are readily diffusible, an assump- 
tion which is not supported by investigation. Magnus (18) says that 
material coming from the insect which may play a part in gall for- 
mation does not have to be readily diffusible, but Kiister (17) says: 
''Das einzige, was wir von den Eigenschaften der von den Cecidozoen 
gelieferten Stoffe wissen, ist, dass sie wasserloslich sind und auf dem 
Wege der Diffusion durch Zahlreiche Zellschichten im Korper der 
Wirtspflanze sich verbreiten konnen." 
Cosens performed several experiments, in which he placed the 
larvae of Amphiholips confluens on starch solutions and after a time 
