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JOUENAL OF THE ROYAL HORTICULTUEAL SOCIETY. 



occur only once. It is therefore hardly possible that such should 

 appear at all among a small number of trial plants ; with some prob- 

 ability, however, we might reckon upon the appearance of a few forms 

 which approach them in the series. 



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 Aqiiilegia atropurpurea canadensis, Laratcra pseiidolhia thurin- 

 giaca, Gcum nrhano-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 dcltoides to the 

 tenth generation, since it regularly propagated itself in the garden. 



With Pisum it was shown by trials 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 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 assimilation and formation of 

 new cells to develop an independent organism. This development 

 follows a constant law, which is founded on the material composition 

 and arrangement of the elements which meet in the cell in a vivifying 

 union. If the reproductive cells be of the same kind and agree with the 

 foundation cell of the mother plant, then the development of the new 

 individual will follow the same law which rules the mother plant. If it 

 chance that an egg cell unites with a dissimilar pollen cell, we must 

 then assume that between those elements of both cells, which determine 

 the mutual differences, some sort of compromise is effected. The re- 

 sulting compound cell becomes the foundation of the hybrid organism, 

 the development of which necessarily follows a different law from that 

 obtaining in each of the two original species. If the compromise be 

 taken to be a complete one, in the sense, namely, that the hybrid 

 embryo is formed from cells of like kind, in w^hich the differences are 

 entirely and permanently accommodated together, the further result 

 follows that the hybrids, like any other stable plant species, remain true 

 to themselves in their offspring. The reproductive cells which are formed 



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

 ■a perfect nnion of the elements of both fertilising cells must take place. How could 

 we otherwise explain that among the offspring of the hybrids both original types 

 leappear in equal numbers and with all their peculiarities? If the influence of the 

 egg cell upon the pollen cell were only external, if it fulfilled the role of a nurse only, 

 then the result of each artificial fertilisation could be no other than that the developed 

 hybrid should exactly reseinble the pollen parent, or at any rate do so very clcsely. 

 Thi3 the experiments so far have in no wise confirmed. An evident proof of the 

 complete union of the contents of both cells is afforded by the experience gained on 

 all sides that it is immaterial, as regards the form of the hybrid, which of the original 

 epecies is the seed parent or which the pollen parent. 



