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. 
1 6 
Srvc 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- 
