246 APPENDIX. 



Until recently it was supposed that all the Cactaceae in the Old World, except 

 Bhipsalis cassytha, which is also American, were colonists descended from American 

 ancestors ; in other words, that there was not a single species of the order peculiar to 

 the Old World. Now we may say that the order, with the exception of one or more 

 species of Bhipsalis, is wholly American, for a very distinct species of this genus has 

 been found in Madagascar*, and probably two or three other forms in the Kew 

 Herbarium from Africa and Madagascar will prove specifically different from B. cas- 

 sytha. With regard to the claims of Opuntia Ficus indica and one or two allied 

 species to be indigenous in the Mediterranean region, adverse opinions have been 

 enunciated ; yet there seems no valid reason to doubt their American origin, seeing 

 how they have spread in South Africa and elsewhere within the knowledge of man, 

 and Mr. A. DeCandolle's special researches confirm this view f. The general dispersion 

 of Bhipsalis cassytha in Tropical America, Africa, the Mascarene Islands, and Ceylon 

 (where it is " certainly indigenous " J) is remarkable ; but its wide area may be due to 

 the agency of birds, as it produces a profusion of small viscid berries. In relation to 

 the distribution of this order it should be stated that we regard the Galapagos as 

 belonging to the American region. One species of Opuntia and one species of Cereus 

 have been collected in these islands ; and Anderson remarks, " Sine dubio plures adsunt 

 species Cactearum, his insulis propriae, quas quidem observavimus ipsi, nee tamen ob 

 angustias temporis eas rite colligere vel depingere licitum fuit. Quatuor vel quinque 

 certe distinctas saltern vidimus " §. 



Bentham and Hooker || distinguish only thirteen genera of the Cactaceae ; but it 

 seems probable, considering the small amount of material they had under examination, 

 that a larger number of types merit this rank. Eleven of these genera are represented 

 within our limits ; two of them being monotypic and restricted to Mexico. Upwards 

 of a thousand proposed species have been described ; but, as explained elsewhere % a 

 large number of them are very imperfectly defined, many of them probably synonyms, 

 and comparatively few of them based upon preserved specimens. 



Mexico is undoubtedly the centre of the Cactaceae, as will presently be shown by 

 figures, and the forms are exceedingly numerous; and it is possible that as many 

 species as have been proposed actually exist ; yet for purposes of comparison it has 

 been considered desirable to deduct about one fifth of them, thus bringing the total 

 down to 500. Even this number may be too high, though not so much so as to affect 

 any question of distribution. One thing is certain, that hybrids are not uncommon, and 



* Baker in Journ. Linn. Soc. xxi. p. 347. 



t L'Origine des Plantes Cultivees, p. 218. 



t Thwaites, ' Enumeratio Plantarum Zeylanise,' p. 129. 



§ Om Galapagos- Oarnes Vegetation, p. 95. 



|| Genera Plantarum, i. p. 846. % Huj. op. i. p. 501. 



