232 M. Cli. Naudin on Eyhridity in Plants. 



the second generation, notwithstanding appearances, still 

 retained some essence of the yellow-flowered Linaria, and 

 this strange particle was sufficient to bring some pollen 

 grains and ovules back either to a mixed state, or altogether 

 to Linaria vulgaris. 



Similar actions are produced, though less marked, in the 

 descent of hybrids of the second generation, which seem 

 entirely returned to the type of L. vulgaris, and even to a 

 certain extent in that of Datura Stramonio-lcevis, where 

 some individuals return to Icevis, preserving up to the third 

 generation the accessory characters which belong to that 

 form of hybrids. All these facts show us that the separa- 

 tion of specific forms allied in hybrids, is not always com- 

 pleted so rapidly as one might be led to suppose, judging 

 from physiognomy and external appearance. 



The return of hybrids to the forms of tbe parent species 

 is not always so sudden as that which we have observed in 

 the Primroses, Petunias, Linaria purpureo-vulgaris, D, 

 3Ieteloido-3Ietel,&c, ; it is frequently completed by insensibly 

 minute gradations continued through long series of genera- 

 tions. We have seen, for example, in Luffa acutangulo- 

 cylindrica, even in the third generation, that among forty 

 individuals only one was found which had wholly reassumed 

 the external appearance of L. cylindrica. 



Hybrids of Nicotiana persica and Langsdorffii, modify 

 themselves slowly, and ten or even more generations may 

 be insufficient to bring them back entirely to the specific 

 forms. 



It is remarkable in the latter case, that the hybrids do 

 not present any appreciable mark of disjunction of the two 

 specific essences, which appear intimately blended together 

 in every part of the plant. Nevertheless the traits of one 

 of the two species sensibly disappear from generation to 

 generation, as if extinguished by degrees ; but it not un- 

 frequently happens that this extinction takes place with 

 such rapidity as to be completed in the second generation. 



En resume^ hybrids fertile and self-fertile return sooner or 

 later to the specific types from which they were derived, 

 and this return is effected either by the separation of the 

 two mixed essences, or by the gradual extinction of one of 



