M. Ch. Naudin on Hyhridity in Plants. 



225 



timia violaceo-nyctaginiflora^ &c. ; and the same in many 

 of the toad-flax hybrids of the third and fourth generations, 

 already very close to Linaria vulgaris. 



In a word, as I said at the commencement of this article, 

 hybrids are found of all degrees of fertility, from the extreme 

 case where the ovary only is fertile to that where all the 

 pollen is as perfect as that of the best-established species. 



(3.) Is the Aptitude of Species to cross each other, and the Fer- 

 tility of the Hybrids ivhich result, proportional to the apparent 

 A^nity of the Species ? 



In general this is the case ; but there are exceptions, and 

 we have stated some. There are, indeed, some species, 

 closely allied in exterior organisation and physiognomy, 

 which are less disposed to mutual crossing than other species 

 which are far distant in their outward appearance. Thus 

 we have seen three species of eatable gourds, so closely re- 

 sembling each other that most botanists fail to distinguish 

 them, resist all attempts to cross them ; whilst the melon 

 and Cucumis trigonus, so very different from one another, 

 easily give origin to very fertile hybrids, though the pollen 

 is a little defective. Such is the case with Nicotiana glauca, 

 which, although very distant from N. angustifolia and 

 macropJiylla, yet gives hybrids with them, having very fer- 

 tile ovaries ; whilst N. glutinosa, more dif&cult to cross with 

 them, although belonging to the same section of the genus, 

 only gives one sterile hybrid both by the pollen and ovary. 

 I might also mention the crossing of D, Stramonium and D. 

 ceratocaula, two species strangers to each other, from which 

 there results a fertile hj^brid, although attended by that 

 peculiar kind of partial sterility which consists in the loss 

 of the first flowers. 



These exceptions, for which it is probably impossible to 

 assign a cause, do not prevent the affinity of species, as re- 

 vealed by the exterior organisation, from indicating generally 

 the degree of aptitude to cross, and do not prevent us from 

 forming a conjecture to a certain extent as to the fertility of 

 the hybrids. We have seen the proof in Datura Meteloido- 

 Metel, D. Stramo7iiO'Tatula and Tatulo- Stramonium, D. Stra- 



