288 PHYSIOLOGY. BOOK II. 



are the most remaikable, there is much room for doubt 

 whether the supposed species upon which the argument is 

 founded ai'e any thing more than wild varieties of each other. 

 The African Gladioh are known to intermix freely ; but 

 Herbert, in his account of them, in the Horticultural Trans- 

 actions, vol. iv. p. 16., admits that he cannot speak to the 

 power of their mides to perpetuate themselves by seed. No 

 botanist can fix positive characters to a large part of the 

 reputed species of Pelargonium, or to the South American 

 Amaryllises ; many of the supposed species of Crinum seem 

 to have no better claim to be so considered than the varieties 

 that might be picked from a bed of tulips ; and, lastly, the 

 Tritica caerulescens, polonicum, and tomentosum, upon which 

 Bellardi's experiments were founded, are plants with the 

 history of which no man is acquainted, and which, in all 

 probability, derive their origin from the Triticum aesti\aim, 

 or common wheat. 



All, I think, that can be conceded upon this subject is, that 

 more hybrid plants are fertile to the third or fourth generation 

 than Kiilreuter supposed, and that the degree of their sterility 

 will depend very much upon the degree of natural relationship 

 which their pai'ents may have possessed. That they will all, in 

 time, revert to one or other of their parents, or become abso- 

 lutely barren, there can be no doubt whatever. 



Although this power of creating mule plants that are fertile 

 for two or three generations incontestably exists, yet in wild 

 nature hybrid varieties are far from common ; or, at least, there 

 are few well-attested instances of their occurrence. Among 

 the most remarkable cases, are the Cistus Ledon, constantly 

 produced between C. monspessulanus and laurifolius; and 

 Cistus longifolius, between C. monspessulanus and populi- 

 folius, in the wood of Fontfroide, near Narbonne, mentioned 

 by Bentham. The same acute botanist ascertained that Saxi- 

 fraga luteopurpurea of Lapeyrouse, and S. ambigua of De 

 Candolle, are only wild accidental hybrids between S. are- 

 tioides and calyciflora : they are only found where the two 

 parents grow together ; but there they form a suite of inter- 

 mediate states between the two. Gentians, having a similar 

 origin, have also been remarked upon the mountains of 



