1886.] NATURAL SCIENCES OP PHILADELPHIA. 321 



Coxe,^ who has had many followers, thought that the hot rays 

 of the sun when acting through a misty or saturated atmosphere 

 deranged the vital activities of the plant and brought about the 

 disease. He considered old varieties more subject to it, on 

 account of having lower constitutional vigor, than new varieties, 

 of which the St. Germain and Seckel were respectively conspicu- 

 ous instances. 



The insect theory, as it was called, was promulgated at this 

 time. It was started upon firm facts by the discovery of a small 

 brown beetle, about two millimeters long, which penetrated the 

 branch, and caused the part beyond to die. The beetle received 

 the name of Scolylus pyri Peck, now changed to Xyleborus pyri 

 Pk., and is still known as the blight beetle. The effect of its 

 attack appears to the casual observer similar to that of the true 

 blight the branch in June or July rapidly withers, and the leaves 

 and fruit turn black. The beetles being minute and inconspicuous 

 escape attention, and the ftict that the branch does not die below 

 a definite point is sometimes overlooked. It is not difficult to 

 see how many persons came to connect this comparatively rare 

 affection with the common fire blight, and to believe that insects 

 of some sort were to be held accountable for all their supposed 

 minuteness and wary habits being sufficient reasons for the failure 

 to find them, and the spread of the disease along the limbs of a 

 tree being ascribed to a poison which the insects were supposed 

 to emit. Among the prominent supporters of this view was the 

 " Genesee Farmer," ^ published at Rochester, N. Y., with Patrick 

 Barry as the horticultural editor. It has not, however, been so 

 strongly advocated for the last decade or two. 



The next hypothesis that attracted general attention was known 

 as the frozen-sap theory. This was based upon the supposition 

 that the autumn or winter freezing of unripe wood produced a 

 poison which the moving currents of sap the next spring and 

 summer distributed, causing the death of the parts. It was first 

 published in 1844 b^^ Rev. H. W. Beecher,^ of Indiana, in a long 

 and able article in " Hovey's Magazine." In the following j^ear 



1 L. c, p. 175. 



^ See Genesee Farmer, vol. vii, 1846, p. 216; vol. viii, 1847, pp. 122, 

 218, etc. 



^ Magazine of Horticulture, vol. x, p, 441. 



