36 CALIFORNIA VEGETABLES. 



The Occurrence of Frosts in California. The occurrence 

 of frost in California is, from one point of view, a purely 

 local question. As has already been stated, the frosty and 

 the frostless places are often in sight of each other on 

 the same landscape from the same point of view. It can 

 be even more closely drawn than that. It is sometimes 

 quite as plainly to be seen as the high-water line of a 

 river flood on a sloping meadow. This occurs of course in 

 what are termed the thermal belts and is determined by 

 elevation, air currents, outflow levels and several other 

 incidents of local topography. There are often wide va- 

 riations in these lines from year to year and yet there is 

 steadfastness enough about the phenomena to enable resi- 

 dents to agree among themselves as to what localities are 

 ' ' in the frost ' ' and what are out of it. Upon this decision 

 depends the business risk in planting out beans, peppers, 

 tomatoes, etc., for winter growth, and it is upon such fields 

 that the frost, not always content with the local definition 

 of its limits, draws the dead line which the morning sun 

 brings into such fateful prominence. Of course the grower 

 is not necessarily content to accept such natural bounda- 

 ries of the thermal belt. He can materially change it all 

 by frost-fighting, but the discussion of that matter be- 

 longs to another chapter. 



It is important to know as nearly as possible the be- 

 ginning and end of the frost free period in each locality, 

 and data to assist in determining this fact are given in 

 the chapter on The Planting Season. 



