188 cnAKvcTEiusTics or the zones of moisture. 



how the presence and absence of these two types affects the general 

 character of the tropical floras. Taking ferns according to the species 

 limitation, and in the sense in which the term is used in the first 

 edition of our ' Synopsis Filicum,' out of 2228 known species 1901, or 

 85 per cent., occur in the tropical zone, and 1437 species, or 65 per 

 cent, of the order, arc confined to it. Out of the genera there are at 

 any rate three, Cheilanthes, Pellsea, and Notochla^na (including to- 

 gether 125 species), which cannot be considered Hygrophilous. But 

 neglecting these, as not materially affecting the result, because many 

 of them are also not tropical, we find practically that the number of 

 ferns in any tropical or sub-tropical flora furnishes an excellent test of 

 the moisture or dryness of the climate of the country. Here are 

 some of the figures. To take first the continents, there are 944 species 

 in Tropical America, 863 in Tropical Asia, 346 in Tropical Africa. To 

 take next countries with an insular climate, there are 320 species in 

 the Himalayas, 118 in Japan, 153 at the Cape, 113 in ^ew Zealand, 

 160 in Australia, 213 in the Mascaren Isles, about 200 in Ceylon, 

 90 in Formosa, 380 in the Polynesian and 630 in the Malayan Isles. 

 Contrast these with the number of species in countries with a conti- 

 nental climate ; Asia Minor 25, Algeria 24, Spain 39, Banda 7, the 

 Punjaub apart from the Hills 11, Italy 40, Arabia Felix 19. In 

 Egypt the only known fern is Adiantum Capillus-veneris. In Nubia 

 there are five, the same Adiantum, jS^otochloena vellea, Onychium 

 melanopus, Actiniopteris radiata, and Ophioglossum vulgatum. lu 

 the neighbourhood of Pekin there are five, Adiantum Edgworthii, A. 

 Capillus-junonis, Cheilanthes argentea, Asplenium japonicum, and 

 A. pekinense. 



In Brazil we have the two kinds of flora displayed side by side 

 under the same latitude, the Hygrophilous type in the ' Pegio dryadum ' 

 of Martius, which belts the coast from the province of Santa Cathe- 

 rina, through Eio Janeiro and Bahia to Pernambuco, and the 

 Xerophilous type in his ' Regio orcadum,' which occupies a large 

 tract in the interior of the country in the provinces of Goyaz, Minus 

 Geraes, and St. Paulo. A great many species and genera are re- 

 stricted to one of the two districts, but there are also a great many 

 other groups and genera which are represented by a large number 

 of impedes in both, as, for instance, in orders Malpighiaceae and Bigno- 

 niaceae, and in genera Eup.itorium, Veronica, Mitraria, and Vitis 

 Echitcs and its allies. The species of these are mostly distinct in the 

 two tracts, and put on so different a type in their vegc^tative organs, 

 that though, of course, when there is a genjric identity there is no 

 sensible difference in flower structure, yet in nineteen cases out of 

 twenty it is easy to see from which tract the plant comes by a mere 

 glance at its texture and general aspect, the rigidity of the leaves or 

 their hairy covering, the shortened petioles, the diminished fl3wers, 

 the congested inflorescence of all of them, the erect stems of tie 

 Malpighiacece and Bignoniaceae, the vanished tendrils of the vines, 

 the greater quantity and rigidity of the pappus-b'istles of the Compo- 

 sitae marking the Oreads from the Dryads. 



Even within the compass of Britain we have the two types con- 

 trasted to a certain extent ; but of the 606 species which in Britain 

 are gradually lost in passing from the south to the north of the 



