114 LUTHER BURBANK 



method of fighting frost by burning brush or oil 

 supplies direct heat, but also supplements this by 

 filling the air with smoke, which retards the radi- 

 ation of heat. 



It is familiarly known that seaboard regions 

 have much milder winters than inland regions of 

 the same latitude. 



Again, inland regions of low altitude, such 

 as the Mississippi Valley, may be adapted to 

 the growth of a fruit that would inevitably 

 winter-kill if grown on the high plateaus of 

 Wyoming. In general, it may be said that 

 no region at higher altitude than about six 

 thousand feet is adapted for general fruit 

 growing. 



In putting out catalogs of new fruit it is often 

 desirable to state the minimum temperature that 

 a new production will stand. As to average an- 

 nual temperature, it may be convenient to recall 

 that there is likely to be a mean annual difference 

 of three degrees for each hundred miles of lati- 

 tude. Thus, for example, the mean temperature 

 at the northern line of Iowa will be found to be 

 about three degrees lower than the mean temper- 

 ature at the southern line; and this difference 

 might, in case of a given fruit, make it folly to 

 plant in northern Iowa a fruit that might live in 

 the southern part of the State. 



