102 THE PLUMS OF NEW YORK. 



There are four phases of temperature that need to be considered in 

 order to get a clear insight into the cUmatic conditions which govern pro- 

 duction of fruit crops. These are, the daily, inonthly and annual changes 

 in temperature and the extremes in temperature. Of these the daily and 

 annual changes are of little importance. All plants are very adaptable to 

 daily variations in climate and are little affected by them. Annual varia- 

 tions are shown by statements of the annual mean temperatures but such 

 statements are of small value to fruit-growers as they may be the result 

 of averaging very divergent temperatures or temperatures very close 

 together. The monthly mean, however, is a very fair criterion of climate 

 for fruit-growing, especially when given with the amount and distribution 

 of rainfall. 



But far more important than any of the above phases are the extremes 

 in temperature and more particularly of cold. A plant can not be grown 

 profitably where the temperature, even occasionally, falls below the 

 point where winter-killing results to tree or bud, or where the blossom 

 is injured by frost. Extremes of heat are disastrous usually only when 

 long continued. For each fruit, too, there must be a total amount of 

 heat available to carry it from the setting of the fruit to maturity, 

 in which respect varieties of any fruit may differ materially. Of the 

 injurious effects and of the necessary amounts of heat, however, we know 

 but little. 



These general considerations of temperature lead us to their applica- 

 tion to the plum and especially to a discussion of the most important of 

 the several factors -hardiness. 



Hardiness to cold, a matter of prime importance with all fruits, is 

 especially so with the plum because of the many different species, each 

 with its own capacity for withstanding cold. As the different species are 

 taken from their natural habitat to other regions, there to become accli- 

 matized, and as new forms originate by hybridization, the matter becomes 

 more complicated and more important. Waugh ' has investigated the 

 hardiness of plums and we publish a table given by him showing the 

 hardiness of representative varieties of the species most generally culti- 

 vated. We have taken the liberty of adding a few plums not given in 

 the original table and have also made some changes in the nomenclature 

 of the groups. 



'Waugh, F. A. Vt. Sta. An. Rpt. 11:273. 1897-9S. 



