December 22, 1905.] 



SCIENCE. 



837 



statements Professor Lloyd has offered a few 

 specific illustrations, as well, to uphold his 

 point, and, if we infer correctly, these are 

 chosen from a great number of cases which 

 he considers applicable. We naturally as- 

 sume, therefore, that they are examples which 

 he thought most conclusive. How well these 

 really substantiate his assertions, however, can 

 only be ascertained by carefully considering 

 the merits of each illustration. And in doing 

 this two predominant questions must be kept 

 clearly in mind: (1) Are we dealing with the 

 most closely related species? (2) Are the two 

 species growing associated under the same 

 conditions ? 



Viewed from this standpoint some of Pro- 

 fessor Lloyd's illustrations not only do not 

 agree with his assumption, but offer excellent 

 examples of the general law suggested by 

 President Jordan. For instance, Viola lanceo- 

 lata and V. primulce folia, we are led to infer, 

 are ass.ociated with each other in the same 

 habitat, a fact upon which at least one well- 

 known authority is very skeptical. But, 

 granting that they do so occur, are they more 

 closely related to each other than to some 

 other species? Three students of the genus 

 whom I have consulted are unanimous in the 

 opinion that they are not. On the contrary, 

 V. lanceolata has its closest relative in V. 

 vittata of the gulf states, while Y. denticulosa,- 

 also of the southern region, holds a similar 

 relation to Y. primulce folia. Both Y. lanceo- 

 lata and Y. primulasfolia, therefore, have 

 their closest relatives not associated with 

 them, but growing in adjoining regions, sepa- 

 rated by one of nature's well-marked barriers, 

 that of temperature. 



Again, Rhodiola integrifolia, it is claimed, 

 occurs associated with R. polygama in Colo- 

 rado, a statement which, it is true, we are 

 unable to refute; but one of the recognized 

 authorities of this genus does not hesitate to 

 assert that R. alashana and not R. polygama 

 is the species nearest R. integrifolia. Both 

 of these occur in Alaska, but there, too, is the 

 barrier intervening; for while R. integrifolia 

 is an alpine plant, R. alashana is confined to 

 the coastal region. 



Fern students will not agree that Dryopteris 



marginalis and D. goldiana are the two more 

 closely related species in that group. On the 

 contrary, D. goldiana is usually considered 

 most closely related to that far northern and 

 western plant known as D. filix-mas. 



If the opportunity were afforded and if we 

 were able to gather the necessary data doubt- 

 less nearly all of Professor Lloyd's examples 

 would be found fully as misleading. Enough 

 have been refuted, however, to clearly show 

 that we are not to accept his statements as at 

 all conclusive. 



Furthermore, our fellow botanist states, as 

 his opinion, that it is easier to find exceptions 

 to President Jordan's rule than facts in sup- 

 port of it. With this assertion we believe it 

 absolutely impossible for any botanist to agree 

 who is at all familiar with plants in the field, 

 or who has ever given the question of geo- 

 graphical distribution any serious considera- 

 tion. The writer most assuredly does not find 

 that difficulty. Many cases among the plants 

 with which he is most familiar in the field are 

 brought to mind; some of which he will take 

 the liberty of presenting for the careful con- 

 sideration of those interested in this general 

 discussion. 



It may be well to state in the beginning 

 that the examples chosen are limited mainly 

 to the flora of the California province, par- 

 tially because the writer is more familiar with 

 the plants of that region, but also because the 

 barriers are more clearly defined there and 

 can be more readily appreciated. 



Among the conifers of the Pacific coast are 

 several suggestive illustrations of the isola- 

 tion theory. For instance, we find Pinus con- 

 torta along the northern seacoast, while on 

 the mountains is its very near relative P. 

 murrayana. Again, Pinus ponderosa of the 

 Pacific slope is represented in the Pocky 

 Mountains by P. scopulorum. Pseudotsuga 

 mucronata is replaced in southern California 

 by P. macrocarpa, while Cupressus macro- 

 carpa of Monterey Bay and C. goveniana of 

 the northern coast ranges of California are 

 two closely related species. 



Gastanopsis chrysophylla of the coast ranges 

 has its nearest relative in C. sempervirens of 

 the Sierra Nevada. The same may be said 



