KELATIONS OB^ THE EUCALYPTS TO CLIMATE. 29 



EELATION OF THE EUCALYPTS TO CLIMATE. 



GENERAL CLIMATIC REaUIREMENTS. 



The Eucalypts dili'er considerably as to the cliuiatic conditions under 

 which the}' thrive, ])ut all the larger arboreal forms agree in requiring 

 a warm climate. Not only do they prefer a climate that is equable, 

 but other conditions must exist in order that the}' may be grown 

 successfully. Prof. Charles Naudin, in his memoir on the genus, 

 gives quite concisel}' the conditions required for the successful growth 

 of Eucalypts. He says: 



The first condition of success in the culture of Eucalyptus is a climate appropriate 

 to their nature; that ia to say, for a great majority of the species, warm summers, a 

 moderate amount of rain, a certain atmospheric dryness, plenty of sunlight, and very 

 temperate winters. 



While all thrive best in regions with warm summers, man}' species 

 do not endure the summer heat of certain sections of southwestern 

 North America. Regions where the midsimuner maximum tempera- 

 tures range from 80^ to 105° F. are best suited to the growth of these 

 trees. Some species thrive in regions where the maximum tempera- 

 tures range in summer from 100° to 120° F., but the number is lim- 

 ited. The various species differ very much as to the ajiiount of cold 

 they will endure. Some will stand minimum temperatures of 10° to 

 15° F., while other species will under no circumstances endure tem- 

 peratures much below freezing. The degree of cold that any species 

 will endure depends not only upon the other conditions of the atmos- 

 phere at the time, but upon the nature of the weather that has pre- 

 ceded. Low temperatures following a warm period that has stimu- 

 lated growth do much more injury than the same degree of cold 

 following a gradual fall in temperature. 



AVhile most Eucalypts are benefited by occasional heavy rainfalls 

 that .saturate the soil thoroughly, frequent rains and a very humid 

 atmosphere are not conducive to their healthful growth. They have 

 the power of absorbing great quantities of water by means of their 

 roots, but the above-ground parts of most species prefer to be in quite 

 dry atmosphere, at least for a portion of the year. A few .species 

 grow in swami)y, humid regions, but the majority of them prefer 

 drier situations. Plenty of sunlight is quite essential to the healthy 

 growth of most species, few of them thriving in the shade of other 

 trees or in regions having nmch cloudy weather. 



CLIMATIC AREAS IN NORTH AMERICA. 



With regard to the eHect of climate upon the Eucalypts, Ave may 

 divide the United States into four sections. In the first and largest 

 division the winters are ordinarily so cold as to kill the Eucalypts, 

 and their growth there outdoors is consequently impracticable. This 



