xiv FLORA OF THE VITIAN ISLANDS. 
The banks of the rivers and rivulets are densely crowded with vegetation, mostly com- 
posed of plants found elsewhere in the group, though not in such a luxuriant state. But 
there are also several species peculiar to these localities, among them Eugenia rivularis, 
Lindenia Vitiensis, Acalypha rivularis, Ficus bambusefolia, Polygonum glabrum, Podocarpus 
bracteata, Eulalia Japonica, Schizostachys glaucifolia, and another undetermined Bam- 
busacea, all of which would have to be classed, physiognomically, with Humboldt's ** Willow 
form,” a set of plants which, unaffected by the occasional rising and turbulence of the 
streams, not only have the same kind of foliage, habit, and mode of growth as genuine 
Willows, but evidently serve the same purpose in Nature’s economy, that of protecting and 
keeping together the river banks, though they are not related to the genus Salix. The 
frequency of plants belonging to this Willow form on river banks in all countries of the 
globe is worthy of more attention than it has as yet received ; and out of it arise, among 
others, the questions :— What possible connection can there be between river banks 
and the so-called Willow form of leaves? Do plants of that kind grow on rivers 
because they have Willow leaves, or do they have Willow leaves because they grow on rivers ? 
It is in fact the old question over again, Does the duck swim because it has webbed feet, 
or has it webbed feet because it swims.* | 
* It would not be difficult to show that most plants bearing leaves of the true Willow form do 
grow by running streams. To say nothing of those species of Salix having Willow leaves, and growing, 
or those Salices not having Willow leaves (S. herbacea, etc.), and not growing by running streams, I would 
direct attention to the different species of Nerium, Epilobium hirsutum (vulgo Anglicé, Willow herb), 
Lythrum Salicaria, Polygonum Persicaria, et sp. pl.; Lindenia rivalis, Astianthus longifolius, ete. That 
many plants are found on rivers which have no Willow leaves has nothing to do with the question, how it 
comes to pass that the Willow form predominates in such localities? Some years ago Dr. Schultz- 
Bipontinus pointed out that in the Composite, the largest Phanerogamous Order, the habit of almost 
every other cropped up again. In Euphorbiacee and other large Orders, similar instances are noted. 
Sometimes this outer resemblance is startling. I remember coming across a Sandwich Island plant which 
looked exactly like Thomasia solanacea, a well-known Buettneriacea, of New Holland, but which, on closer 
examination, proved to be a variety of Solanum Nelsoni, the resemblance between the two being as 
striking as that pointed out in Bate’s ‘ Travels on the Amazon,’ between a certain moth and a humming 
bird. These outer resemblances between different species which have no organic relationship, have 
played us Botanists many a trick, and have been the cause of some otherwise incomprehensible synonyms 
;n our systematic works—Daviesias having been described as Acacias, Cycads as Ferns, and Veronicas 
as Conifers, by really good botanists relying too implicitly upon them,—resemblances to which the 
term * Mimicry in Nature” has been applied. I have objected (‘ Gardeners’ Chronicle,’ 1868, June 27, 
and ‘ Journal of Botany,’ 1868, p. 213) to this term, because, in applying it either in zoology or botany, 
the whole question here cropping up is prejudged, it being assumed that (1) organisms have the power to 
mimic other organisms; and (2) that they have come in contact with those organisms which they are 
supposed to mimic. I suggested the term “ Outer resemblances.” Mr. Leo H. Grindon has since proposed 
that of * Echoes," and given a popular illustration of it (‘Echoes in Plant and Flower Life, London, 
F. Pitman, 1869, 117 pp); but the term is more poetical than scientifically correct, as an echo is simply 
a repetition, more or less distinct, of one and the same utterance, which the “echoes” here meant are 
