TRANSAQTIONS OP THE SECTIONS. 109 



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

 indeed states it to be " a remarkable peculiarity that the indigenous flowers are, 

 with very slight exceptions, all perfectly 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 Wahlenben/ias, several C'omposiUe, and especially 

 the handsome red flowers of the now almost extinct forest-trees, the ebony and 

 redwood (species of Melhania, Byttneriaceas). 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 iu the fertilization of these gaily-coloured flowers. The researches of Dr._ 

 Hermann Miiller have shown us by what minute modifications of structure or of 

 fimction many flowers are adapted for partial insect- andself-feitilization in various 

 de^^rees ; so that we have no difficulty in understanding how, as the insects diminished 

 and finally disappeared, self-fertilization 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 connexion with this subject is the presence of arbo- 

 rescent forms of Compcsitffi in so many of the remotest oceanic islands. They 

 occur in the Galapngos, in Juan Fernandez, in St. Helena, in the Sandwich Islands, 

 and in New Zealand ; but they arenotdiiectly related to each other, representatives 

 of totally different tribes of this extensive order becoming arborescent in each 

 group of islands. The iinmen.se range and almost universal distribution of the 

 Compositte is due to the combination of a great facility of distribution (by their 

 seeds) with a gieat attractiveness to insects, and the capacity of being fertihzedby 

 a variety of species of all orders, and especially by flies and small beetles. Thus 

 they would be among the earliest of flowering plants to establish themselves on 

 oceanic islands ; but where insects of all kinds were very scarce it would be an 

 advantage to gain increased size and longevity, so that fertilization at an interval 

 of several years might suffice for the continuance of the species. The arborescent 

 form would combine with increased longevity the advantage of increased size m 

 the struggle for existence with ferns and other early colonists; and these advantages 

 have led to its being independently produced in so many distant localities, whose 

 chief feature in common is their remoteness from continents and the extreme 

 poverty of their insect life. • , i. • 



As the sweet odours of flowers are known to act in combination with their 

 colours, as an attraction to insects, it might be anticipated that where colour was 

 deficient scent would be so also. On applying to my friend Dr. Hooker for infor- 

 mation as to New-Zealand plants, he informed me that this was certainly the case, 

 and that the New-Zealand flora is, speaking generally, as strikingly deficient in 

 sweet odours as in conspicuous colours. Whether this peculiarity occurs in other 

 islands, I have not been able to obtain information ; but we may certainly expect 

 it to be so in such a marked instance as that of the Galapagos flora. 



Another question which here comes before us is the origin and meaning of the 

 odoriferous glands of leaves. Dr. Hooker informed me that not only are New- 

 Zealand plants deficient in scented flowers, but equally so in scented leaves. This 

 led me to think that perhaps such leaves were in some way an additional attrac- 

 tion to insects — though it is not easy to understand how this could be, except by 

 adding a general attraction to the special attraction of the flowers, or by supporting 

 the larvaj which, as perfect insects, aid in fertilization. Mr. Darwin, however, 

 informs me that he considers that leaf-glands bearing essential oils are a protection 

 against the attacks of insects where these abound, and would thus not be required 

 in countries where insects were very scarce. But it seems opposed to this view 

 that highly aromatic plants are characteristic of deserts all over the world, and in 

 such places insects are not abundant. Mr. Stainton informs me that the aromatic 

 Labiatte enjoy no immunity from insect attacks. The bitter leaves of the cherry- 



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



