No. 494] 



THE LAW OF GEMINATE SPECIES 



79 



species are closely related, suggesting mutants, and in 

 other cases the relation indicates the existence of hybrids. 

 In California, for example, there are in the same general 

 region many species of Lupinus, of Calochortus, of Ceano- 

 thus, of Arctostaphylos, of Esehscholtzia, of Godetia, of 

 CEnothera, and Opuntia. Eucalyptus, Acacia and Epa- 

 cris in Australia are examples even more striking. But 

 I have never seen very closely related or geminate forms 

 in any of these genera actually growing together. I sus- 

 pect that they do so sometimes and that the explanation 

 is found in reinvasion. But " growing together" is an 

 indefinite statement as applied to plants. The elder, the 

 alder and the madrono (arbutus) abound in the Santa 

 Clara Valley. But no one ever saw any two of these 

 trees standing side by side. Each has its limitations, as 

 to soil and moisture. 



Setting aside these genera which are represented by 

 many species in a limited area, and among which muta- 

 tion and hybridism may be conceivably factors in species- 

 forming, we find the law of geminate species applying to 

 plants as well as to animals. Crossing the temperate zone 

 anywhere on east and west lines, we find species after 

 species replaced across the barriers by closely related 

 forms. Illustrations may be taken anywhere among the 

 higher plants— equally well, no doubt, among lower ones. 

 Many genera are local in their distribution, monotypic— 

 with a single species, the origin of which can not be traced. 

 But many other genera belt the earth or come very near 

 doing so, each form or species being geminate as related 

 to its next neighbor. This fact is illustrated in Rubus, 

 Alnus, Sambucus, Platanus, Fagus, Veratrum, Symplo- 

 carpus, Symphoriearpus, Castanea, Quercus, Pinus, 

 Tsuga, Acer, Rhus, Pyrus, Primus, Lonicera, Ranuncu- 

 lus, Trientalis, Lilium, Trillium, Veronica, Aquilegia, 

 Gentiana, Viola, Epilobium, Pteris, Mimulus, Trifolium, 

 Solidago, Aster. All these genera and many others fur- 

 nish an abundance of examples. 



We may, therefore, say that with plants as well as ani- 

 mals geminate species as above defined owe their dis- 



