NATURAL OEDERS. 147 



tinent of India, from Ceylon, New Holland, and even from 

 the Island of St. Vincent. 



Acrostichum stemaria of M. de Beauvois,^ which hardly 

 diflFers from A. alcicorne of New Holland, and of several 

 of the islands of the Malayan Archipelago, was also ob- 

 served ; and Acrostichum aureum, which agrees with speci- 

 mens from equinoctial America, was found growing in 

 plenty among the mangroves near the mouth of the river. 



I have formerly observed that the number of Filices, 

 unlike that of the other Cryptogamous orders, (Lycopodinese 

 excepted,) is greatest in the lower latitudes ; and, as I then 

 supposed, near or somewhat beyond the tropics. The latter 

 part of this statement, however, is not altogether correct ; 

 the maximum of the order, both in absolute and relative 

 number of species, being more probably within the tropics, 

 though at considerable heights. 



The degree of latitude alone being given, no judgment 

 can be formed respecting the proportion of Pilices : for 

 besides a temperature somewhat inferior, perhaps, to im 

 that of equinoctial countries of moderate elevation, a humid 

 atmosphere and protection from the direct rays of the sun, 

 seem to be requisite for their most abundant production. 



When all these conditions co-exist, their equinoctial 

 proportion to Phsenogamous plants is probably about one to 

 twenty, even on continents where the tracts most favourable 

 to their production form only a small part, their number 

 being increased according as such tracts constitute a more 

 considerable portion of the surface. 



Hence their maximum appears to exist in the high, and 

 especially the well wooded, intratropical islands. Thus in 

 Jamaica,' where nearly two hundred species of Perns have 

 been found, their proportion to Phsnogamous plants is pro- 

 bably about one to ten. In the Isles of France and Bourbon, 

 from the facts stated by M. du Petit Thouars,^ they appear 

 to be about one to eight. 



In Otaheite, according to Sir Joseph Banks's observations, 



' More d'Oioare \, p. 2, t. 2. 



^ Melanges de Bot. Observ. add. a IL de lamarch, p. 6, e( 38. 



