220 POMOLOGY 



for much damage may occur from too low or too high tem- 

 peratures during the winter rest. The latter are treated in 

 Chapter XL 



Many fruit sections are accmnulating data on which fu- 

 ture plantings may be based with greater intelligence. The 

 mean amiual temperature or the mean of the 365 successive 

 daily means is a figure of importance for any given place, as 

 is also the mean temperature of the hottest six weeks. The 

 annual mean is frequently computed from the twelve monthly 

 means which is practically the same as when calculated 

 on the daily basis. The average dates of the last frost in 

 spring and the first frost in autumn are also of great im- 

 portance to the pomologist and vegetable-gardener. From 

 these figures is calculated the average number of days free 

 from frost at any particular point, and hence the length of 

 the average growing season. 



The total temperature necessaiy for the development of 

 plants or for the accomplishment of any phase of their 

 growth has been a question of interesting speculation for 

 many years and has resulted in an attempt to secure the 

 "physiological constant" for a plant, which is discussed in a 

 later paragraph. The general temperature conditions for the 

 larger regions of this countiy are indicated in paragraph 198. 



From the standpoint of the pollination and "setting" 

 of fruit, temperature is of vital importance and this is treated 

 more fully in connection with pollination of fruits (Chapter 

 XII). Aside from actual injury to the floral parts, partic- 

 ularly the pistils from frosts and low temperatures, the 

 development of the pollen-tube may be checked materially 

 when the temperature falls below 50° F. The bees are not 

 active much below 65° F. and hence the opportunity for 

 pollination of the flowers is greatly reduced when the tem- 

 perature remains constantly below that point during the 

 period of blossoming. 



