in Hybridisation 87 



each of the two original species would occur only once. It 

 is therefore hardly possible that these should appear at all 

 among a small number of experimental plants ; with some 

 probability, however, we might reckon upon the appearance 

 in the series of a few forms which approach them. 



We meet with an essential difference in those hybrids 

 which remain constant in their progeny and propagate 

 themselves as truly as the pure species. According to 

 Gartner, to this class belong the remarkably fertile hybrids 

 Aquilegia atropiirpiirea canadensis, Lavatera pseiidolbia 

 tJwringiaca, Geum urbano-rivale, and some Dianthus 

 hybrids ; and, according to Wichura, the hybrids of the 

 Willow species. For the history of the evolution of plants 

 this circumstance is of special importance, since constant 

 hybrids acquire the status of new species. The correctness 

 of this is evidenced by most excellent observers, and cannot 

 be doubted. Gartner had opportunity to follow- up Dianthus 

 Armeria deltoides to the tenth generation, since it regularly 

 propagated itself in the garden. 



With Pisum it was shown by experiment that the 

 hybrids form egg and pollen cells of different kinds, and that 

 herein lies the reason of the variability of their offspring. 

 In other hybrids, likewise, whose offspring behave similarly 

 we may assume a like cause ; for those, on the other hand, 

 which remain constant the assumption appears justifiable 

 that their fertilising cells are all alike and agree with the 

 foundation-cell [fertilised ovum] of the hybrid. In the 

 opinion of renowned physiologists, for the purpose of 

 propagation one pollen cell and one egg cell unite in 

 Phanerogams* into a single cell, which is capable by 



* In Pisum it is placed beyond doubt that for the formation of the 

 new embryo a perfect union of the elements of both fertilising cells 

 must take place. How could we otherwise explain that among the 



