Sept. 7, 1876] 



NATURE 



407 



climate and perennial moisture. In this respect, however, Tahiti 

 can hardly differ greatly from many other islands, which yet have 

 no such vast preponderance of ferns. This is a question that 

 cannot be decided by mere lists of species, since it is probable 

 that in Tahiti they are less numerous than in some other islands 

 where they form a far less conspicuous feature in the vegetation. 

 The island most comparable with Tahiti in that respect is Juan 

 Fernandez. Mr. Moseley writes to me — " In a general view of 

 any wide stretch of the densely-clothed mountainous surface of 

 the island, the ferns, both tree-ferns and the unstemmed forms, 

 are seen at once to compose a very large proportion of the mass 

 of fohage." As to the insects of Juan Fernandez, Mr. Edwyn 

 C. Reed, who made two visits and spent several weel?s there, 

 has kindly furnished me with some exact information. Of butter- 

 flies there is only one {Pyrameis carte), and that rare — a Chilian 

 species, and probably an accidental straggler. Four species of 

 moths of moderate size were observed — all Chilian, and a few 

 larvse and pupae. Of bees there were none, except one very 

 minute species (allied to Chilicola), and of other Hymenoptera, 

 a single specimen of Ophion hiteus — a cosmopolitan ichneumon. 

 About twenty species of flies were observed, and these formed 

 the most prominent feature of the entomology of the island. 



Now, as far as we know, this extreme entomological poverty 

 agrees closely with that of Tahiti ; and there are probably no 

 other portions of the globe equally favoured in soil and climate 

 and with an equally luxuriant vegetation, where insect-life is so 

 scantily developed. It is curious therefore to find that these two 

 islands also agree in the wonderful predominance of ferns over 

 the flowering plants^ — in individuals even more than in species, 

 and there is no difficulty in connecting the two facts. The 

 excessive minuteness and great abundance of fern-spores causes 

 them to be far more easily distributed by winds than the seeds 

 of flowering plants, and they are thus always ready to occupy 

 any vacant places in suitable localities, and to compete with the 

 less vigorous flowering plants. But where insects are so scarce, 

 all plants which require insect fertilisation, whether constantly to 

 enable them to produce seed at all, or occasionally to keep up 

 tlaeir constitutional vigour by crossing, must be at a great dis- 

 advantage; and thus the scanty flora which oceanic islands must 

 always possess, peopled as they usually are by waifs and strays 

 from other lands, is rendered still more scanty by the weeding 

 out of all such' as depend largely on insect fertilisation for their 

 full development. It seems probable, therefore, that the pre- 

 ponderance of ferns in islands (considered in mass of individuals 

 rather than in number of species) is largely due to the absence 

 of competing phenogamous plants ; and that this is in great 

 part due to the scarcity of insects. In other oceanic islands, 

 such as New Zealand and the Galapagos, where ferns, although 

 tolerably abundant, form no such predominant feature in the 

 vegetation, but where the scarcity of flower-haunting insects is 

 almost equally marked, we find a great preponderance of small, 

 green, or otherwise inconspicuous flowers, indicating that only 

 such plants have been enabled to flourish there as are independent 

 of insect fertilisation. In the Galapagos — which are perhaps 

 even more deficient in flying insects than Juan Fernandez — this 

 is so striking a feature that Mr. Darwin speaks of the vegetation 

 as consisting in great part of *' wretched-looking weeds," and 

 states that '* it was some time before he discovered that almost 

 every plant was in flower at the time of his visit." He also says 

 that he "did not see one beautiful flower" in the islands. It 

 appears, however, that Compositse, Leguminosae, Rubiacese, and 

 Solanaceje, form a large proportion of the flowering plants, and 

 as these are orders which usually require insect fertilisation, we 

 must suppose either that they have become modified so as to be 

 self-fertilised, or that they are fertilised by the visits of the 

 minute Diptera and Hymenoptera, which are the only insects 

 recorded from these islands. 



In Juan Fernandez, on the other hand, there is no such total 

 deficiency of showy flowers. I am informed by Mr. Moseley 

 that a variety of the Magnoliaceous winter's bark abounds, and 

 has showy white flowers, and that a Bignoniaceous shrub with 

 abundance of dark blue flowers, was also plentiful ; while a white- 

 flowered liliaceous plant formed large patches on the hill-sides. 

 Besides these there were two species of woody C«mpositse with 

 conspicuous heads of yellow blossoms, and a species of white- 

 flowered myrtle also abundant ; so that, on the whole, flowers 

 formed a rather conspicuous feature in the aspect of the vegeta- 

 tion of Juan Fernandez. 



But this fact — which at first sight seems entirely at variance 

 •with the view we are upholding of the important relation between 

 the distribution of insects and plants — is well explained by the 



existence of two species of humming-birds in Juan Fernandez, 

 which, in their visits to these large and showy flowers fertilise 

 them as effectually as bees, moths, or butterflies. Mr. Moseley 

 informs me that " these humming-birds are extraordinarily 

 abundant, every tree or bush having one or two darting about 

 it." He also observed that " nearly all the specimens killed 

 had the feathers round the base of the bill and front of the head 

 clogged and coloured yellow with pollen. " Here, then, we have 

 the clue to the perpetuation of large and showy flowers in Juan 

 Fernant'.ez ; while the total absence of humming-birds in the 

 Galapagos may explain why no such large-flowered plants have 

 been able to establish themselves in those equatorial islands. 



This leads to the observation that many other groups of birds 

 also, no doubt, aid in the fertilization of flowers. I have often 

 observed the beaks and faces of the brush-tongued lories of the 

 Moluccas covered with pollen ; and Mr. Moseley noted the same 

 fact in a species of Artatnus, or swallow-shrike, shot at Cape 

 York, showing that this genus also frequents flowers and aids in 

 their fertilisation. In the Australian region we have the immense 

 group of the Meliphagidse, which all frequent flowers, and as 

 these range over all the islands of the Pacific, their presence will 

 account for a certain proportion of showy flowers being found 

 there, such as the scarlet Metrosideros, one of the i^"^ conspicuous 

 flowers in Tahiti. In the Sandwich Islands, too, there are forests 

 oi Metrosideros ; and Mr. Charles Pickering writes me, that they 

 are visited by honey-sucking birds, one of which is captured by 

 sweetened bird-lime, against which it thrusts its extensile 

 tongue. I am also informed that a considerable number of 

 flowers are occasionally fertilised by humming-birds in North 

 America ; so that there can, I think, be little doubt that birds 

 play a much more important part in this respect than has hitherto 

 been imagined. It is not improbable that in Tropical America, 

 where this family is so enormously developed, many flowers will 

 be found to be expressly adapted to fertilisation by them, just as 

 so many in our own country are specially adapted to the visits of 

 certain families or genera of insects. 



It must also be remembered, as Mr. Moseley has suggested to me, 

 that a flower which had acquired a brilliant colour to attract insects 

 might, on transference to another country, and becoming so modi- 

 fied as to be capable of self-fertilisation, retain the coloured petals 

 for an indefinite period. Such is probably the explanation of the 

 Pelargonium of Kerguelen's land, which forms masses of bright 

 colour near the shore during the flowering season ; while most of 

 the other plants of the island have colourless flowers in accord- 

 ance with the almost total absence of winged insects. The 

 presence of many large and showy flowers among the indigenous 

 flora of St. Helena must be an example of a similar persistence. 

 Mr. Melliss indeed states it to be "a remarkable peculiarity that 

 the indigenous flowers are, with very slight exceptions, all per- 

 fectly colourless ; " ^ but although this may apply to the general 

 aspect of the remains of the indigenous flora, it is evidently not 

 the case as regards the species, since the interesting plates of 

 Mr. Melliss's volume show that about one-third of the indigenous 

 flowering plants have more or less coloured or conspicuous 

 flowers, while several of them are exceedingly showy and 

 beautiful. Among these are a Lobelia, three Wahlenbergias, 

 several Compositce, and especially the handsome red flowers of 

 the now almost extinct forest-trees, the ebony and redwood 

 (species of Melhania, Byttneriaceie). We have every reason to 

 believe, however, that when St. Helena was covered with 

 luxuriant forests, and especially at that remote period when it 

 was much more extensive than it is now, it must have supported 

 a certain number of indigenous birds and insects, which would 

 have aided in the fertilisation of these gaily-coloured flowers. 

 The researches of Dr. Hermann Midler have shown us by what 

 minute modifications of structure or of function many flowers aref 

 adapted for partial insect- and self-fertilisation in varying degrees, 

 so that we have no difficulty in understanding how, as the insects 

 diminished and finally disappeared, self-fertilisation may have 

 become the rule, while the large and showy corollas remain to 

 tell us plainly of a once different state of things. 



Another interesting fact in connection with this subject is the 

 presence of arborescent forms of Compositse in so many of the 

 remotest oceanic islands. They occur in the Galapagos, in 

 Juan Fernandez, in St. Helena, in the Sandwich Islands, and 

 in New Zealand; but they are not directly related to each other, 

 representatives of totally different tribes of this extensive order 

 becoming arborescent in each group of islands. The immense 

 range and almost universal distribution of the Compositas is due 

 to the combination of a great facility of distribution (by their seeds), 

 I Melliss's St. Helena, p. 226, note. 



