THE EXTINCTION OF SPECIES. 



products of crossing, take the place of the parent-stocks, so that the only remark that 

 need be added here is that when such substitution is observed in the case of plants 

 belonging to successive geological periods, it seemed as though a gradual re-casting 

 or moulding of the species had taken place, and was regarded as a phenomenon 

 determined by the direct effects of variations of climate until the time when the 

 great importance of crossing in relation to the genesis of new species began to be 



recognized. 



The partial extinction of a species, i.e. its disappearance from particular parts of 

 its area of distribution, must be distinguished from complete extinction. Of the 

 numerous instances of partial extinction within our knowledge some have been due 

 to intentional or unintentional extermination by mankind, but the majority are cases 

 where purely local extinction has resulted from natural causes independently of 

 human influence. Reference has repeatedly been made in these pages to cases of 

 plants which grow in the midst of now reigning floras and yet do not belong to 

 them, and they have been likened to outposts left behind by former occupants of 

 the soil, being apparently the remains of floras which formerly flourished on the 

 areas in question, but which have been turned out and forced to take refuge in 

 neighbouring regions. If their displacement were due to climatic vicissitudes it is 

 conceivable that separate species or even entire communities may have been left 

 behind here and there in especially favourable, though possibly very restricted 

 habitats, and such isolated spots then seem as though they had been wrested from 

 the main area of distribution which stretches over a wide expanse of country in the 

 vicinity. Interesting examples of this are afforded by several species which are 

 confined to isolated habitats in Carniola, of which the " Konigsblume " (Daphne 

 Blagayana) may be selected as a type. This plant grows on the slopes of some 

 mountains in the neighbourhood of Laibach. Before the flora of the Balkan Penin- 

 sula had been accurately explored it was believed that this species of Daphne 

 had no other habitat than that on the mountains above mentioned. More recent 

 botanical researches have, however, revealed the fact that the main area of distribu- 

 tion of Daphne Blagayana is really in the Balkan Peninsula, in Bosnia and Servia, 

 and that the habitat in Carniola is to that area as an island to the mainland. 

 When one sees by what a small number of individuals, amounting to some thousands 

 only, this curious plant is represented in Carniola, and how rare it is for even these 

 to bring fruits to maturity owing to the fact that autogamy is impeded and that 

 the supply of insect-visitors is insufficient, there is no escape from the conviction 

 that a series of very severe winters would be enough to cause its complete extermi- 

 nation in this district. Under such circumstances its existence in the main area of 

 istribution in the Balkan Peninsula might not be in any way imperilled, for it is 

 :ely that the particular causes to which the extinction of the species in the 

 ream Carniola would be due would operate in all the habitats in the larger 



i, which is hundreds of kilometres away. 



That such phenomena as have here been suggested as possible and even probable 

 e of Daphne Blagayana do actually happen is evidenced by the plant- 



