738 



being fertilized by the pollen of the hybrid, or vice versa, a mixed 

 race may be kept np for some time longer ; but it will then have a 

 manifest tendency to return to the form of the parent whose interven- 

 tion has been employed." " Amongst animals the limits of hybridity 

 are more narrow, since the hybrid is totally unable to continue its race 

 with one of its own kind ; and although it may be fertile with one of 

 its parent species, the progeny will of course be nearer in character to 

 the pure blood, and the race will ultimately merge into it." " One or 

 two instances have been mentioned, in which a mule has, from union 

 with a similar animal, produced offspring ; but this is certainly the 

 extreme limit, since no one has ever maintained that the race can be 

 continued further than one generation, without admixture with one of 

 the parent species."* So writes Professor Carpenter, one of the most 

 satisfactory authors that could be cited as setting forth the received 

 opinions on the best and most recent authorities. 



As regards that part of the opinion which has reference to the ani- 

 mal kingdom, I am enabled to state a very interesting case in point, 

 observed by my relative, Professor Bell. A few years since, he kept 

 specimens of both sexes of the common domestic goose and the swan- 

 goose {Cygnus Guineensis). They readily bred together; and a race 

 of hybrids was the result. He watched very closely, to observe whe- 

 ther the hybrids would breed among themselves. This was never the 

 case in any one instance, though both male and female hybrids bred 

 readily with the other sex of both the pure breeds ; the resulting pro- 

 geny of course more nearly approximating to the pure species than 

 did the first hybrids. This, therefore, is entirely confirmatory of the 

 received laws of hybrids, as set forth above in the words of Dr. Car- 

 penter. Not so, however, were two instances which have occurred to 

 myself in reference to plants. 



Ten years ago I instituted some experiments, not with any refe- 

 rence to testing the opinions on the laws of hybridization, but to 

 ascertain the value of certain forms of British plants as species. The 

 plants in question appear in our Floras as species ; but I had a sus- 

 picion they were hybrids. The plants are Epilobium roseum and 

 Geura intermedium. The former I suspected, in common with an 

 opinion at one time held by the late Sir James Edward Smith, to be 

 a hybrid between Epilobium raontanum and E. tetragonum,t though 



* ' Principles of Physiology, General and Comparative,' by W. B. Carpenter, 

 M.D., F.R.S., &c., 3rd edit. p. 983. 



t Eng. Bot. vol. X. tab. 693, 1800. Sir James Smith here writes, speaking of 

 Epilobium roseum: — "Is it possible to have arisen from seeds of the latter" (E. 



