RECAPITULATION OF THE DOMINANT FEATUKES OF THE FLOEA. 311 



absent orders are:— (1) Resedaceae, (2) Vochysiaceae, (3) Frankeniaceae, (4) Elatineae, 

 (5) Chailletiaceae, (6) Santalaceae, and (7) Gnetaceae. Of these the first is probably 

 not represented in America by any indigenous species; the second and fifth are 

 tropical extensions into Guatemala; and the remaining four, which are known to 

 exist in North Mexico, though very small groups, are widely spread, and may yet be 

 found in South Mexico. Nearly 78 per cent, of the genera known from the three 

 provinces occur in South Mexico, and more than 65 per cent, of the species; and as a 

 more exact investigation is likely to raise rather than lessen these totals, it may safely 

 be inferred that this is one of the densest concentrations of plants in any part of the 

 world where the greater part of the area is within temperate regions. The numbers of 

 orders and genera exceed those for the whole of Australia, and the number of species 

 is within 500 of the total known to inhabit Australia in 1881*. 



The orders absolutely or relatively (that is in relation to the whole order) numerous 

 either in genera or species, or both, are : — Polygalaceae (30 sp.) ; Malvaceae (20 gen., 

 110 sp.) ; Malpighiaceae (13 gen., 55 sp.); Burseraceae (27 sp.); Sapindaceae (14 gen., 

 57 sp.); Leguminosae (84 gen., 564 sp.) ; Rosaceae (21 gen., 72 sp.); Crassulaceae 

 (47 sp.) ; Melastomaceae (22 gen., 82 sp.) ; Lythraceae (65 sp.) ; Onagrarieae (11 gen., 

 68 sp.); Loasaceae (5 gen.); Passifloraceae (39 sp.); Cucurbitaceae (22 gen., 74 sp.); 

 Begoniaceae (46 sp.) ; Cactaceae (370 sp.) ; Compositae (157 gen., 977 sp.) ; Asclepiadeae 

 (17 gen., 100 sp.) ; Gentianaceae (10 gen., 43 sp.) ; Polemoniaceae (5 gen., 14 sp.); 

 Hydrophyllaceae (4 gen., 18 sp.); Convolvulaceae (108 sp.) ; Solanaceae (18 gen., 

 162 sp.); Scrophularineae (33 gen., 104 sp.); Gesneraceae (12 gen., 49 sp.); Acan- 

 thaceae (29 gen., 110 sp.); Verbenaceae (16 gen., 69 sp.) ; Labiatae (23 gen., 200 sp.); 

 Nyctagineae (10 gen., 26 sp.); Piperaceae (136 sp.); Loranthaceae (42 sp.); Euphor- 

 biaceae (25 gen., 259 sp.) ; Urticaceae (21 gen., 89 sp.) ; Cupuliferae (72 sp.) ; Orchideae 

 (82 gen., 504 sp.) ; Bromeliaceae (64 sp.) ; Amaryllideae (12 gen., 128 sp.); Dioscoreae 

 (20 sp.); Liliaceae (73 sp.); Palmae (12 gen., 50 sp.); Aroideae (45 sp.); Cyperaceae 

 (170 sp.) ; Gramineae (91 gen., 454 sp.) ; and Filices (42 gen., 379 sp.). 



It has already been explained (page 307) how the number of Cactaceae and other 

 succulent plants attributed to this province may have been augmented at the expense 

 of North Mexico. With these probable exceptions, the foregoing figures are as 

 accurate as could be desired, and betoken an extraordinary richness and plasticity in 

 the flora. Setting aside those characteristic of a dry climate, we find evidence of an 

 enormous development in certain groups of plants which flourish only where there is 

 considerable humidity. These are the plants that inhabit the eastern slopes and 

 ravines, and constitute what we should call the special flora of this province, in contra- 

 distinction to the southward extensions of the North-Mexican flora. We rank this as 

 a distinct floral province, and it is perhaps the more convenient and logical course that 

 we could adopt ; yet here northern and southern types meet and commingle in a most 



* Engler, Versueh, ii. p. 34. 



