APPENDIX. xix 



Mr. Sessions. A great obstacle is in procuring help you can 

 depend on. 



Professor Riley. Let me make one other suggestion. While 

 the infested area is stated in the rough at fifty square miles, from 

 what Pi'ofessor Shaler said there would probably be large portions 

 of it that would require nothing but inspection. Now, wherever 

 there are large trees difficult to climb, I would certainly take the 

 precaution to ring or band them, because that will prevent any 

 stray caterpillars from climbing up those trees. No caterpillars 

 will ascend such trees ; and if any escape, you will find them at 

 the foot of the trees. European experience shows this. • 



Professor Shaler. Where can we get on the track of the mixt- 

 ure they use in Europe for that purpose ? 



Professor Riley. You can use printers' ink for that purpose. 

 In Newark I recommended the use of the fire department for 

 spraying certain very tall elm trees. 



Professor Shaler. I presume we could make such an arrange- 

 ment with the fire departments. 



Mr. Craig. We have an engine that could be so used. 



Professor Riley. I would modify my objection to egg collect- 

 ing just so far that in the case of large trees it would be advisable 

 to do the work prior to aestivation. I think boys could go over 

 them, and in this direction winter work would be advisable. It 

 would also be advisable to have these large trees very carefully 

 inspected for the eggs ; but I do not believe you would be justified 

 in attempting to destroy the eggs over the whole area. 



Professor Shaler. Is the energy of diffusion and the tendency 

 of the females to travel at all proportioned to their numerousness ? 



Professor Riley. Yes ; it is a general principle with insects 

 that, in proportion as they become unduly multiplied, the migra- 

 tory instinct is developed. 



Professor Shaler. So that, in so far as we reduce the number 

 in a given field, we tend to reduce the expansive energy? 



Professor Riley. Without doubt. 



Professor Shaler. And, therefore, if we fail to exterminate it 

 this year, we shall at least diminish its expansive energy. 



