TRANSACTIONS OF SECTION D. — DEPT. ZOOLOGY AND BOTANY. 665 



scribed in general monograplis and scattered papers, and adding to tliem those that 

 we possess in the London herbaria alone, we have now definite knowledge from 

 Madagascar of not less than 2,000 species, wliich the author estimates represent 

 700 genera and 125 natural orders. The tiora, as a whole, follows closely the same 

 general lines as that of the other tropical countries of the old world. This maj- be 

 illustrated in various ways. The annexed table gives the number of genera'and 

 species of each order in Madagascar as compared with Mauritius, continental 

 tropical Africa, and India, apart from the Himalayas, and it will be seen that the 

 general parallelism is very close. 



Out of 55 known orders of Thalamiflorae only eight are not here represented ; but 

 of these 47, 37 are already known in Madagascar. Of the ten orders not yet known 

 in Madagascar, none are known in Mauritius, but two are represented by single 

 species in the Seychelles. Two of them are confined to Tropical Asia and one to 

 Tropical Africa, but the other seven are common to both continents. 



One of the most striking and suggestive characters of the flora of the intertropical 

 zone of tlie world, taken as a whole, is the large extent to which it is everywhere 

 made up of species representing large genera which are spread through it pretty 

 evenly. There are many genera containing 300, 400, or 500 species, that are largely 

 represented in Africa, Asia, and America. Some of these are herbaceous glumi- 

 ferous monocotyledons, as, for instance, (''yperus with 400 species, and Panicum 

 with 500. The large genera of ferns, such as Polypodium, Acrostichum, Asplenium, 

 and Pteris, all fall into this category. Some of them are dicotyledons with sepa- 

 rated sexes and small inconspicuous "flower-wrappers, such as Ficiis with 400 species, 

 Piper with GOO, Phyllanthus with 400-500, Croton with 450. But many of these 

 large cosmopolitan genera are dicotyledons of shrubby or arborescent habit, with 

 insect-fertilised hermaphrodite flowers, a distinct calyx and corolla, and showy, 

 scented petals. Loranthus with 300 species, although exclusively parasitical, falls 

 into this category. So do Psychotria with 500 species, Indigofera with 300-400, 

 •Vernonia with 400, Solanum with 500, and Eugenia with 500. And a point which 

 must be prominently taken into account in estimating the general relations of the 

 flora of Madagascar, is that nearly all these large cosmopolitan genera are now 

 ascertained to be represented in the island, although often by endemic species. 



The marked tendency to uniformity in character which is shown by the flora of 

 the whole tropical zone is further illustrated by the fact that a considerable number 

 of species are spread universally through the old world, and that a considerable 

 number extend their range to Tropical America. Of the plants of our own colonies 

 in that part of the world, out of 1,058 flowering plants and vascular Cryptogamia, 

 370, or about one-third, occur both in Tropical Asia and Continental Africa, and 

 225 species, or about one in five of the total flora, extend their range to Tropical 

 America. In Madagascar the absolute number of these widely-spread species is as 

 great, but of course the proportion which they bear to the total flora is smaller. 

 Tlie orders most largely represented here are Cyperacese, Gramineff, Compositse, 

 Leguminospe, and Malvacese. 



In the island flora there are altogether abotit 80 endemic genera, according to 

 our present knowledge. The order Chlfenacese has been supposed to be peculiar to 

 Madagascar, but two of the genera have been found in Mozambique. The otlier 

 genera are many of them monotypic, and very few contain more than tliree or four 

 species. They are not concentrated in any part of the systematic series, and most 

 of them belong to tlie large natural order.s, Compositte with nine genera, and Paibia- 

 cere with eight, taking the lead. 



^Vith Mauritius, Bourbon, and the Seychelles the affinity of the Madagascar 

 flora is close. There are several genera and species which occur both in the large 

 and small islands which are restricted to the group. 



There is a close affinity between the flora of Madagascar and that of Tropical 

 Africa. In Rubiacere, for instance, there are nine genera otherwise confined to 

 Tropical Africa whicji reach Madagascar, and in other orders a smaller number, 

 "We have instances of such genera in Brexia, Dombeya, Acridocarpus, Psorosper- 

 mum, Myrothamnus, Psiadia, I.andolphia, and Mimulopsis. Instances of striking 

 species common to both areas are furnished by Haronga madagascarensis, Trachy- 



