Because of this rare occurrence, among tropical fruits, of fine horticultural varieties as compared with the profusion of semi-wild seedlings, much criticism has been ignorantly directed at these fruits in general. C. F. Baker, who has done much to advance the science of tropical pomology, graphically states the case as follows:

"On hearing some aspersions cast upon the caimite (Chryso-phyllum Cainito), a valuable and delicious fruit at its best, a Cuban was heard to remark, 'There are caimites, and there are caimites!' A similar remark might be made of most tropical fruits. The methods of seed selection, of breeding, and of vegetative propagation have rarely been brought to bear on any of these things. As for systematic search for the better forms now existing, and the rapid building up of really comprehensive experimental plantations of them in the tropical botanic gardens and experiment stations, we have yet a field of highly useful, most remunerative, and intensely interesting work before us."

It is to this field that attention must be devoted, if the agricultural development of the tropics is not to become even more one-sided than it is to-day. British horticulturists in India and Ceylon, French in the Oceanic colonies, and American in the subtropical parts of California and Florida, as well as in the West Indies, Hawaii, and the Philippines, have done notable work during the past quarter of a century; yet when their achievements are considered alongside the possibilities, it is evident that hardly has a beginning been made with this promising field.

"Botanicus verus," said the great Linnaeus, "desudabit in augendo amabilem scientiam," - "The true botanist will sweat in advancing his beloved science." Even so must the investigator who undertakes to further the progress of tropical pomology expect to find hard work, at times under trying climatic conditions, - to sweat indeed, - unless his lot is cast in the delightful climate of the tropical highlands, or in subtropical regions such as California and Florida. But the subject is one which offers such a wealth of fascinating problems and gives promise of such valuable results, that for a long time to come it can hardly fail to attract the needful few among the many whose tastes incline them toward pomological pursuits.

It is indeed fortunate for our country that its boundaries include areas where certain of the most valuable tropical fruits can be cultivated. Of these areas, the warmer parts of Florida and California seem destined, by reason of their favorable situation with respect to the great centers of our population, to take the lead in the production of such fruits for supplying the northern markets. The advantageous climate of these states as regards living and working conditions, as compared with the tropics, makes it probable also that they will be the 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 perfection 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, however, 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 not grow where the temperature falls much below 40° (where temperatures are mentioned in this work, they refer to the Fahrenheit scale) are here termed strictly tropical; by tropical plants are meant (following P. H. Rolfs) those of the zone in which the coconut can be grown; and by subtropical plants, those of the zone of the orange. The next region, in point of minimum temperatures, should be termed the semi-tropical, but this term is frequently confused with subtropical and had better be avoided by stretching the use of the word subtropical to cover the region in which the loquat, the pomegranate, and the date can be grown. It must be borne in mind, however, that knowledge regarding the frost-resistance of plants is still meager. Because a certain species has safely passed through a temperature of 25° above zero in a particular instance in California, it need not follow that the plant will withstand the same temperature in another region, nor even that the same individual specimen in California would withstand again 25° if in different physiological condition.

With a few exceptions, the common names for the fruits are those recommended by the American Pomological Society (Proceedings 1917). The pomological nomenclature (names of fruit varieties) also follows, so far as is possible, the Code of Nomenclature of that Society. In spelling names which have come into the English from the Arabic or some other oriental alphabet, the system has been followed elaborated by the International Congress of Orientalists at Geneva in 1894, and now generally adopted by those having to do with the transliteration of oriental names; which is, that vowels should take the value they possess in Spanish and other Latin languages, and consonants the value they possess in English. The names in this work most affected by the application of this principle are those of varieties of the mango, date, and pomegranate, and the common names of a few minor fruits. Current spellings rejected as incorrect are given in the synonymy of varieties.

The botanical nomenclature is intended to conform to the International Rules, better known as the Vienna Rules. These are the ones followed by European, as well as many American, botanists. In the botanical synonymy all names are included which commonly appear in the publications of the United States Department of Agriculture, when they differ from those adopted under the Vienna Rules.