222 EXPEPvIMExNT STATION. [Jan. 



tioiis tbe following varieties as of sufficient hardiness to endure 

 the severe winters of that State : ^ — 



Of the first degree of hai'diness, Oldenburg, Hibernal, Charlamofif, 

 Patten, Okabena. 



Of tlie second degree of hardiness, Wealthy, Tetofski, Malinda, Peer- 

 less, Northwestern Greening. 



Many other sorts thrive in the more favorable parts of this 

 belt, but the great bulk of the varieties grown in localities of 

 similar summer temperatures in the east perish from winter- 

 killing. The minimum winter temperatures in this territory, 

 according to the records of the Weather Bureau,- are around 

 — 40° F., which may be considered a degree of cold which any 

 tree of Pyrus mains can rarely endure without injury (see Fig. 

 15). It should be borne in mind that this temperature must 

 be taken in accordance with the methods of the Weather Bureau 

 and with correct instruments, else the figures obtained are likely 

 not to be comparable. 



The Heat of Summer. — A glance at the figures (Figs. 6-14) 

 giving the distribution of varieties shows that some extend the 

 entire length of its belt, while others succeed well only through 

 the eastern portion. There are three differences between the 

 eastern and western portions of these belts. Tn the west we find 

 (1) lower humidity, (2) less precipitation, (3) more severe 

 heat during the summer. Probably all these have their influ- 

 ence in limiting the western spread of certain varieties, for their 

 effects on the plant are similar, in that they tend to dry it out. 

 In relative importance the greater heat is probably of the great- 

 est significance followed by rainfall and humidity. 



The Effects of Low and High Mean Summer Temperatures. 

 — The effects on the fruit of a low summer heat, as indicated 

 by the mean summer temperature, are as follows : — 



7. Greater Acidity. — It is shown that the acidity of the 

 fruit steadily decreases all through the stages of growth, ripen- 

 ing and decay. It naturally follows that if the fruit does not 

 have time to mature properly it will be acid, and this is clearly 

 shown in the table of analyses. 



1 Report, 1907, p. 34. " United States Weather Bureau, Bulletin Q. 



