The pomelo is by the same author considered to be indigenous to the Pacific Islands east of Java, the citron and affiliated species to have originated in India, and the sour orange east of India, and all to have been in cultivation for over two thousand years. The antiquity of the orange and mandarin is less, both species being from China and Cochin China.
All these species have been introduced into the Philippine Archipelago, and are well distributed excepting the sour orange, which is rarely seen. The discussion of all species refers to them as found in the Philippines except when otherwise stated.
No very distinct types are found among the oranges or mandarins; the variation in the pomelo is considerable, although, so far as the writer has noted, scarcely enough to warrant the distinction of separate varieties. Both the white and red-fleshed types occur with many gradations, but no studies have been made to note which other correlative characters, if any, are identified with these different forms. The very primitive pomelos ([Pl. II, c]) that are not infrequently seen in cultivation might indicate that this species is indigenous to the Philippines, though so far as the writer knows the tree has never been seen in the virgin forest. Closer observations have been made on the general type represented by the citron, including the lemon and lime, and several distinct forms have been recognized.
The calamondin, C. mitis Blanco, is well known to be indigenous, as well as the cabuyao and related plants that have been referred to C. histrix DC. In the first-named species there seem to be no very marked variations.
C. histrix was described by De Candolle, flowers and fruits excepted, from a plant growing in Montpellier, being recognized principally by its long broad-winged petioles and free stamens. The writer has not had the opportunity to see the original description of C. histrix or examine the type specimen, but Swingle refers to it in Jour. of Agri. Research, Vol. I, No. 1, page 10, 1913, as having broadly winged petioles, often larger than the blades, the wings being more gradually narrowed toward the base and usually more abruptly truncate at the tip than C. ichangensis Swingle, making then somewhat triangular in outline.
Within these broad limitations a number of otherwise remarkably distinct forms may be recognized some of which were illustrated in a previous publication, Bureau of Agriculture Bulletin No. 27, Citriculture in the Philippines, 1913, and referred to C. histrix with the statement that “some of these forms unquestionably will be recognized as subspecies on closer study, or possibly as separate species.” Since then several plants of this type in the citrus collection assembled at Lamao by the Bureau of Agriculture have bloomed and fruited, affording an opportunity for fuller observations, and these have been further complemented during a trip to Bohol and Cebu in May, 1914, and by the fruits forwarded by Mr. E. F. Southwick.
However, assuming that C. histrix (or some of its subspecies) is the C. histrix of De Candolle, there still remain, on one hand the limao, and on the other the biasong, balincolong, samuyao, samuyao-sa-amoo, as widely different from each other and the cabuyao and its subspecies as for instance the orange, and pomelo, or the mandarin and the calamondin. A very interesting characteristic has been discovered in several of the citrus fruits that have free stamens in the form of a more or less distinct nucleus in the juice cells; this, so far as the writer knows, has not been previously recorded in a citrus fruit. The fact that the presence of these nuclei is not here referred to in some species with free stamens does not necessarily mean that they are absent, considering that fruits of these particular species have not been examined since the first nuclear cells were discovered. The writer is inclined to believe that these nuclei are correlative to those species having free stamens.
To the student in the citrus-growing sections of the United States the characterization of the citron, lemon and lime as given herein is no doubt satisfactory, but in the Philippines various forms called “limon” will appear that do not agree with this and it would then be necessary either to make the descriptions more general so as to cover the additional forms or to classify these as species or subspecies. If the barely margined petioles, comparatively small leaves, the green, tender growth and the white corolla are insisted upon for the lime, for instance, it is difficult to know where to place the purple-growthed, thorny, wide-winged, purplish-petaled, subglobose limes with wide-winged leaves of the Philippines. They cannot well be placed with the lemons, and still less with the citron, though they of course show strong relationship to each. The citron group of the genus perhaps more than any other shows the need of further study and systematization of the entire genus.
Attention should be called to the presence in the Philippines of the extremely primitive types of the citron and the lemons; for instance, the fruit illustrated in Bulletin No. 27, Plate XVI (c), and colo-colo, as well as the lombog, referred to C. pseudolimonum in this paper.
Of all the plants here discussed, C. micrantha var. microcarpa is botanically furthest removed from the cultivated citrus fruits.