226 M. Cb. Naudin on Hyhridity in Plants. 



monio-kevis, Nicotiana texano-rustica and rustico-texana, N. 

 angustifoUo-macrophylla, &c. , which hybrids, with the marked 

 exception of those of D. Stramonium, have perfect fertility. 

 The aptitude of species for mutual impregnation, and the 

 degree of fertility of the hybrids which result, are therefore 

 the true signs of their special affinity as regards generation ; 

 and in the great majority of cases this affinity is indicated 

 by the exterior organisation — in other words, by the phy- 

 siognomy of the species. 



(4.) On the Physiognomy of Hybrids. 



To give a just idea of the aspect which hybrids present, 

 it is essential to distinguish between the first generation 

 and those which follow. 



I have always found in those hybrids which I have ob- 

 tained myself, and whose origin has been w^ell known to 

 me, a great uniformity of aspect between individuals of the 

 first generation, no matter how numerous, provided they 

 proceed from the same crossing. This we have seen in 

 Petunia violaceo-nyctaginiflora, Datura Tatulo-Btramonium, 

 and D. Stramonio-Tatula, D. Meteloido-Metel^ D. Stramonio- 

 Icevis, Nicotiana texano-rustica, and N. rusticp-texana, N. 

 persico-Langsdor£ii, &c. 



I do not mean to say that all the individuals of the same 

 crossing are absolutely counterparts of one another ; there 

 are sometimes slight variations between them, but not suf- 

 ficient to alter the general uniformity in a sensible degree, 

 and it does not appear to me that these differences are any 

 greater than those which are frequently seen between the 

 seeds of legitimate species of the same production. In 

 short, it may be said that hybrids which proceed from 

 the same crossing, resemble each other, in the first gene- 

 ration, as much as, or nearly as much as those which pro- 

 ceed from the same legitimate species. 



Must it be admitted, as M. Klotzsch maintains, that 

 mutual hybrids (those whicli proceed from the two possible 

 crossings between the two species) are markedly difi'er- 

 ent from each other ; for example, the hybrid obtained 

 from the species A fertilised by the s]>ecies B, differs sensi- 



