242 POMOLOGY 



of the fruit-belt and indicates the isothermal lines as they 

 locate the last killing frosts of the spring. The tempered 

 effect along this littoral region is due to the prevailing winds 

 passing over Lake Michigan during most of the winter and 

 spring months. In the spring the winds are kept continually 

 cool in passing over the lakes and hence prevent unseason- 

 able advancement of the fruit-buds in April and May 

 which results in disastrous effects in unprotected regions. 

 On the other hand, the winter winds that leave the Wiscon- 

 sin shore at a temperature of thirty to forty degrees below 

 zero arrive on the Michigan side at a temperature of little 

 if any below zero, since the waters of the lake rarely freeze 

 over and are connnonly some three to five degrees above 

 the freezing point. While a minimum range of ten to fifteen 

 degrees below zero may be recorded along the northern sec- 

 tion of this "belt," it may be thirty or forty degrees below 

 zero in the north-central counties of the state. 



210. Effect of climate on the floral structure. — Climate 

 may have a veiy definite effect on the floral structure and 

 more particularly on the vitality of the parts of the flower. 

 A long and serious controversy was waged in the early his- 

 tory of strawberiy-growing in this country (1850-70) on 

 the sexual characters of this fruit. In some sections cer- 

 tain varieties were perfect flowering and in others the same 

 kinds were imperfect. That the climate had affected them 

 in this way was later discovered. The same is true with 

 the strawberry grown in eastern United States and in Eng- 

 land, where in the latter place the mild, humid climate some- 

 times causes imperfect flowering sorts to become perfect. 



The Bartlett pear, which is usually self-sterile, is reported 

 by Garcia to be sufficiently self-fertile to insure fair crops 

 of fruit in New Mexico. Likewise in California it was found 

 that the Bartlett is self-sterile on the high elevations and 

 partially self-fertile in the valleys. 



