6 MANUAL OF TROPICAL AND SUBTROPICAL FRUITS 



field of more activity along lines of horticultural investigation 

 than will the strictly tropical countries where the fruits are 

 native. Of course, it is not possible to cultivate within the 

 boundaries of the continental United States all of the fruits 

 discussed in this work. Many of them are uncompromisingly 

 tropical in character and refuse to accommodate themselves to 

 regions where the temperature ever falls as low as the freezing 

 point. It is a noteworthy and hopeful circumstance, however, 

 that certain of the tropical fruits attain their greatest per- 

 fection when grown at the extreme northern or southern limit 

 of their zone, when pushed, so to speak, right up against the 

 frost-line. For example, the citrus fruits have been brought 

 in California and Florida to a higher degree of excellence than 

 has been reached by them in strictly tropical regions. 



It has been thought in the past that it might be possible, by 

 means of a process of acclimatization, to adapt even the more 

 tender species of tropical plants to conditions in California and 

 Florida, and ultimately to cultivate them on a commercial 

 scale in those states. In the light of present knowledge, how- 

 ever, it seems probable that ability to withstand frost is not 

 greatly increased by submitting a plant to lower temperatures 

 than those to which it has been accustomed, even when this 

 is carried through several consecutive generations, and the 

 chances of acclimatizing in California such fruits as the strictly 

 tropical annonas are not great. 



Many of the tropical fruits have as yet scarcely been brought 

 under cultivation, and systematic cultivation of the more 

 important ones, such as the avocado and mango, is of such 

 recent origin that cultural practices have not yet become 

 standardized. New developments are constantly taking place. 

 It is, therefore, inevitable that many of the practices herein 

 described will be obsolete a few years hence. 



Regarding the use of the terms tropical and subtropical a 

 few words of explanation are necessary. Plants which will 



