OF WASHINGTON. 287 



among other things, I failed, in my paper, to point out the im 

 portant fact that the Transition forms a barrier to certain species 

 coming from the East, and that such cannot reach Ohio by natu 

 ral spread ; that Upper Austral forms are quite as likely to reach 

 Ohio from the East by means of the great commercial paths to 

 middle western New York and thence by natural spread through 

 lower Ontario and southern Michigan, or by lake from Buffalo 

 to Cleveland, Sandusky, or Toledo, as by commercial jumps 

 across the mountain regions of Pennsylvania. 



In reply to these three separate indictments I will say that I 

 have a profound regard for truths, fundamental or otherwise, 

 when they have been proven to be such, but not w T hen based on 

 negative evidence. I did, in my paper, point out the fact that 

 the Allegheny mountains formed an impassable barrier to some 

 species, and that such had probably been introduced by the way 

 of our trunk lines of railways in the transportation of articles of 

 commerce. I did not term the barrier " transition life-zone," but 

 gave some instances where the introductions were on the line of 

 the railways. Now, commercial jumps, it seems to me, are all 

 right provided we do not lean too heavily on them and use them 

 as a solution of problems in geographical diffusion where they do 

 not belong. In other words, we must exercise the utmost caution 

 against being misled by them, and assume that their influence 

 has been greater than it really has. It will be observed that I 

 do have a little faith in " commercial jumps," which I could not 

 possibly have if I were to concur with friend Howard in his third 

 proposition. In this case I am, most assuredly, on the side of 

 44 commercial jumps," for it will not be at all difficult to prove 

 that insects have reached Ohio, in some instances, by this avenue, 

 while of the two others mentioned by Mr. Howard, in one case 

 they have not, and in the other they cannot. I confess that, as I 

 look over Dr. Merriam's map of life-zones, I cannot see why 

 eastern species of insects should not pass westward through 

 Ontario and southern Michigan, into Ohio, as indicated by Mr. 

 Howard, but the fact that they do not remains stubbornly in the 

 way. There is not a case on record where an eastern species has 

 appeared in northwestern Ohio before it did in the eastern section. 

 Then, too, Lake Erie looks as though it might convey some 

 species from Buffalo to Cleveland, or even beyond. But there is 

 a slow but steady movement of the water toward Buffalo instead 

 of from it, and evidence of which may be found in the fact that 

 the sewage of Cleveland contaminates the water of the lake for 

 some distance to the eastward, but not to the westward. Then, 

 again, the high winds that might aid in this method of transpor 

 tation during the season when insects are most likely to be car- 



