PEACH YELLOWS. ♦ 273 



ations. Between badly infected districts and uninfected ones there is also a 

 middle ground in which may be found some affected trees or orchards. 



These facts are all opposed to the Goessman Penhallow theory. There is, 

 however, a still more serious objection. 



If yellows is due to soil-exhaustion, the most convincing proof should be 

 found in localities where the action of other presumptive causes, e. g., con- 

 tagium, freezing, etc, have been reduced naturally or artificially to a mini- 

 mum. Manifestly it will not do to accept affirmative evidence on this point 

 from sections of the country where several supposed causes are acting unre- 

 strainedly at the same time, and ^ny one of which may be the true cause. 

 For this reason the whole Atlantic coast may be ruled out, and also a large 

 part of the Northwest. In all this region either the winters are severe, or 

 the disease is not present, or it is allowed to spread without any general, 

 systematic effort to check it. The only localities really suitable for such an 

 inquiry are (1) those parts of the South where the climate is mild and the 

 disease has never appeared, and (2) the peach belt of western Michigan, close 

 to the lake shore, in the vicinity of South Haven, Van Buren county, and in 

 the townships of Oasco, Ganges, and Saugatuck, Allegan county, where the 

 yellows law is enforced and where the lake tempers the severity of the winters. 



The soil in many parts of the South was "exhausted " years ago, and yet 

 peach trees continue to be comparatively free from yellows, and often live 

 twenty or thirty years. However, as I am more intimately acquainted with 

 conditions in Michigan, I will confine the discussion to that region. 



The four Michigan townships named border Lake Michigan for a distance 

 of twenty-four miles, and comprise the most important peach district in the 

 state, the only one at all comparable with the peach regions of New Jersey, 

 Maryland or Delaware. The country has not been well settled more than 

 thirty or forty years, and there is still considerable virgin forest of pine, hem- 

 lock, beech, and maple. The character of the soil varies from a light sand 

 to a heavy clay loam. At South Haven, and generally near the lake, it is 

 sandy. Some miles inland, at least in Allegan county, the soil is heavier and 

 more fertile. 



In accordance with state law, supported in this region by a very strong 

 public sentiment based on a nearly universal belief in the communicable 

 nature of yellows, diseased peach trees are cut down or dug out and burned 

 as soon as discovered. In this way, on the theory of spread by contagion the 

 infective material, whatever it may be, must presumably be kept at a mini- 

 mum. If it is developed in the tree it can never be very abundant, for there 

 are never very many diseased trees in existence at any one time. The prox- 

 imity of Lake Michigan also tends to prevent injury by freezing. 



Here, then, the influence of two supposed causes is reduced to a minimum, 

 and the effect of soil exhaustion will, if anywhere, be freed from complications, 

 and in condition to be estimated more nearly at its true value. 



The fact that cases of yellows still appear in this [region, year after year, 

 in spite of the modifying influence of the great lake, and in spite of the com- 

 paratively strict enforcement of the law, would, at first, seem to favor the 

 theory of soil exhaustion, but really does not. Some very stubborn facts stand 

 in the way of the acceptance of this theory. These are : 



(1) Yellows is much less prevalent where the law has been strictly enforced. 

 This phase of the question will be considered later at some length under "In- 

 35 



