268 APPENDIX. 



species; but what is more remarkable they comprise upwards of 400 species more 

 than the Gramineee, the next order below them ; hence it may be confidently assumed 

 that they will maintain this position, and possibly even take the second place where 

 the Leguminosee now stand. In Mexico and Central America, taken together, orchids 

 form 8 per cent, of the species of phanerogamic plants, and 37 per cent, of the 

 monocotyledons. Taking South Mexico alone, the most thoroughly explored part of 

 our area, they constitute about 30 per cent, of the monocotyledons. The percentage 

 of orchids in monocotyledons for the whole world is about 28 ; that is reckoning the 

 species of the former at 5000, which is certainly none too high. Assuming the number 

 of orchideous genera to be 350, we have 30 per cent, of them in Mexico and Central 

 America, and about 18-8 per cent, of all the species. Out of 105 genera only fourteen 

 are actually restricted to our limits. Three extend into western North America ; six 

 into eastern ; sixty into the West Indies, and eighty-two into South America ; but of 

 the remainder only fifteen extend beyond America. Ten of these, which are nearly all 

 of terrestrial habit, are of wide distribution ; two (Epidendrum and Govenia) are repre- 

 sented in the Galapagos, two (Bletia and Arethusa) in China and Japan, and Physurus in 

 tropical Asia. Of the widely diffused genera, the terrestrial genus Spiranthes, limited 

 to the section Euspiranthes, specially deserves mention as having the widest range of 

 any orchid type. It is found in America from the Arctic regions to Chili, including 

 the West Indies ; and the only orchid in the Bermudas is a Spiranthes. In the Old 

 World the genus is generally spread, except in Tropical and South Africa; and 

 S. amtralis has the widest area and is the commonest of all species of orchids, as it 

 extends from Afghanistan and China to Australia and New Zealand. Spiranthes 

 romanzoviana, a common North- American species, is elsewhere only found in county 

 Cork*, Ireland. A specimen in the British Museum, purporting to have been 

 collected by Pavon in Mexico, has been identified as this species by Mr. Ridley. 



Coming to the species of orchids within our limits, we find that 800 out of 938, 

 or 85 per cent., are endemic; figures unapproached by any other large order, 

 except the Composite, which is 5 per cent, lower. An examination of the distri- 

 bution table (p. 195) further shows that the endemic element is proportionately much 

 stronger in Mexico and Guatemala than it is in the southern area. Looking at the 

 distribution within Mexico, it is very striking and surprising how rapidly the numbers 

 decrease northward, or rather, it would be more correct to say, how suddenly orchids 

 cease almost altogether. From what we know of the routes of the various collectors, 

 whose plants are not localized in herbaria, we may safely add the " Uncertain " column 

 to South Mexico, which gives 500 species for this region. Turning to the North- 

 Mexican column there is a total of only twelve species. This extremely low number 

 seemed to demand a second examination of the data ; and the result of this examination 



* Or perhaps we should state was found, for there are reports of its recent destruction through the land 

 being ploughed. 



