172 ESSAYS. 



Barely two dozen ; and three or four of these are more or less 

 maritime. Only two or three of them extend west of the Mississippi 

 Valley. 



Narthecium is not in the list, a form or near ally of the European 

 and Atlantic-American species having been detected in Japan ; the 

 genus is unknown on the Pacific side of our continent. 



II. 



Since the foregoing tables were prepared, a letter from Mr. Dall 

 (who has returned from an arduous and successful exploration of the 

 Alaskan region, made under the authority of the United States Coast 

 Survey) informs me that his party met with Caulophyllum upon one 

 of the Shumagin Islands. These islands lie off the southern shore 

 of the peninsula of Alaska, about in latitude 55°, longitude 160°. 

 No specimen occurs in the beautiful collection of dried plants made 

 in this expedition, mainly by Mr. Harrington ; nor indeed any other 

 plants which affect so southern a range as our Caulophyllum. Yet 

 the plant may well have been rightly identified ; although it should 

 be seen by botanists before any conclusions are drawn from it. But 

 the occurrence of an intermediate station like this would probably 

 lead Professor Grisebach to rank the north Asiatic Caulophyllum 

 no longer as a representative species, but as identical with our At- 

 lantic plant, as Miquel and Maximowicz, as well as myself, have 

 already done upon evidence derived from the specimens. 



Then, — upon Professor Grisebach's idea that, while identical 

 species are to be referred to a single origin and the disseverance 

 accounted for through means and causes now in operation, repre- 

 sentative species have somehow arisen independently under similar 

 climates, — Caulophyllum must be explained as a case of migration, 

 but Diphylleia (in the same predicament, only with a perceptible 

 difference between the two plants) as a case of double origination. 

 So of the Shortia galacifolia and the Schizocodon uniflorus, of 

 which the corolla and stamens in both are still wanting. If these, 

 when found, should prove to be exactly alike in the two, the very 

 difficult problem of accounting for the world-wide separation under 

 present circumstances is to be encountered ; if a difference appears, 

 the problem is to consider how, and upon what, similar climates can 

 have acted to have originated almost identical species upon opposite 

 sides of the world. Professor Grisebach's views imply that " each 

 species has arisen under the influence of physical and other external 

 conditions," and that gradual alterations in a climate somehow pro- 



