IMPORTANCE OF ADEQUATE HEAT 19 



These records will show any one familiar with winter killing of 

 the leading orchard fruits that such disasters are not to be feared 

 in the chief fruit regions of California. Local temperature is largely 

 controlled by local conditions, as has been already pointed out, and 

 in the districts named in the table there are special locations where 

 the lowest temperature probably differed a few degrees from the 

 figures given. 



NECESSITY OF ADEQUATE SUMMER HEAT 



Passing beyond the freedom from winter killing, it may be re- 

 marked that the influences of certain degrees of heat upon the growth 

 of the plant and the perfection of its fruit, has been the subject of 

 much close observation. Boussingault conducted careful experiments, 

 and showed that a temperature above a certain minimum of heat is 

 found necessary for germination, another for chemical modification, 

 and a third for flowering, a fourth for the ripening of seeds, a fifth 

 for the elaboration of the saccharine juices, and a sixth for the 

 development of aroma or bouquet. 



Originally the mean annual temperature was alone observed, and 

 the polar limits of plants, it was presumed, could be thereby deter- 

 mined. More recently it was taught that the mean temperature of 

 seasons is of more importance than that of the year, and it is believed 

 that to the relative distribution of heat over the seasons rather than 

 to the absolute amount received during the year, we are to attribute 

 the fitness or unfitness of a region for the growth of certain kinds 

 of vegetation. 



It is held in Europe that the mean heat of the cycle of vegetation 

 of the vine must be at least 59 degrees Fahr., and that of the summer 

 from 65 degrees to 66 degrees Fahr. It is stated to be impossible, 

 for instance, to cultivate the vine upon the temperate tablelands of 

 South America, where they enjoy a mean temperature of 62.6 de- 

 grees to 66.2 degrees Fahr., because these climates are characterized 

 by a constancy of temperature, never rising to the higher heats nec- 

 essary to the process of sugar forming, and the vine grows and 

 flourishes, but the grapes never become thoroughly ripe. Boussin- 

 gault shows that, in addition to a summer and autumn sufficiently 

 hot, it is indispensable that at a given period that which follows the 

 appearance of seeds there should be a month the mean temperature 

 of which does not fall below 66.2 degrees Fahr. As will appear 

 presently, this temperature test should not be taken alone, but it will 

 serve as a standard to show one feature of the horticultural adapta- 

 tion of the California climate. Boussingault claims the need of 66.2 

 degrees Fahr. for a single month. To be sure to include this, the 

 accompanying table gives the average summer temperature at the 

 leading fruit-growing centers named. 



