September 21, 1876. ] JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 



255 



months ago they wera small plants in pots about 3 feet high. 

 They were th9n planted out in a bed in the large conservatory, 

 and the leaves now extend to a height of about 24 feet. They 

 are two of the finest specimens in the conservatory. The 

 substance they are growing in is nothing but pure loam, and 

 Mr. Edmonds, the gardener, attributes their rapid growth to 

 the great quantities of wat9r with which they have been sup- 

 plied throughout the summer. — Visitok. 



ASSOCIATION of PLANTS, BIRDS, and INSECTS. 



At the recent meeting of the British Association Mr. A. R. 

 Wallace delivered a lecture, from which the following is ex- 

 tracted : — 



Ever since Mr. Darwin showed the immense importance of 

 insects in the fertilisation of flowers great attention has been 

 paid to the subject, and the relation of these two very different 

 classes of natural objects has been found to be mora universal 

 and more complex tuan could have been anticipated. Whole 

 genera and families of plants have been so modified as first to 

 attract and then to be fertilised by certain groups of insects, 

 and this special adaptation seems in many cases to have de- 

 termined the more or less wide range of the pla*ts in question. 

 It is also known that some species of plants can be fertilised 

 only by particular species of insects, and the absence of these 

 from any particular locality would neoessarily prevent the con- 

 tinued existence of the plant in that area. Here, I believe, 

 will be found the clue to much of the peculiarity of the floras 

 of oceanic islands, sinc9 the methods by which these have 

 been stocked with plants and insects will be often quite dif- 

 ferent. Many seeds are, no doubt, carried by oceanic currents, 

 others probably by aquatic birds. Mr. H. N. Moseley informs 

 me that the albatrosses, gulls, puffins, tropic birds, and many 

 others nest inland, often amidst dense vegetation, and he 

 believes they often carry seeds attached to their feathers from 

 island to island for great distances. In the tropics they often 

 nest on the mountains far inland, and may thus aid in the 

 distribution even of mountain plants. Insects, on the other 

 hand, are mostly conveyed by aerial currents, especially by 

 violent gales; -and it may thus often happen that totally un- 

 related plants and insects may be brought together, in which 

 case the former must often perish for want of Euitable insects 

 to fertilise them. This will, I think, account for tho strangely 

 fragmentary nature of these insular floras, and the great 

 differences that often exist between those which are situated 

 in the same ocean, as well as for the preponderance of certain 

 orders and genera. 



The unusual proportion of Ferns is a general feature of in- 

 sular as compared with continental floras ; but it has, I believe, 

 been generally attributed to favourable conditions, especially 

 to equable elirnat9 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 which cannot be decided by mere lists of 

 species, since it is probable that in Tahiti they are less nume- 

 rous thau in some other islands where they form a far less 

 conspicuous feature in the vegetation. The island most com- 

 parable with Tahiti in that respect is Juan Fernandez. 



Now, as far a3 we know, the extreme entomological poverty 

 of Juan Fernandez 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 diffioulty iu connecting the two facts. The excessive 

 minntenes3 and great abnndauoe 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. Bat 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 their constitutional vigour by crossing, must be at 

 a great disadvantage ; and thus the scanty flora which oceanic 

 islands must always possess, peopled as they usually are by 

 waifs and stray3 from other lands, is rendered still more scanty 

 by tho weeding-out of all such as depend largely on insect 

 fertilisation for their full development. It seems probable, 

 therefore, that the preponderance of Ferns in islands (con- 

 sidered in mass of individuals rather in number of species) is 



largely due to the absence of competing phasnogamons'plants'; 

 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 pre- 

 dominant 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 — whioh 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 oonsiBting 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 he " did not see 

 one beautiful flower" in the islands. It appears, however, 

 that Composite, Leguminosre, Rubiaceae, and Solanaoeae form 

 a large proportion of the flowering plants, and as these are 

 orders which usually require insect fertilisation, we must sup- 

 pose either that they have become modified so as to be self- 

 fertilised, or that they are fertilised by the visits of the minute 

 Dipteras and Hynienopterss, which are the only insects reoorded 

 from these islands. 



In Juan Fernandez, on the other hand, there is no suoh 

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

 Moseley that a variety of the Magnoliaceons Winter's Bark 

 abounds, and has showy white flowers, and that a Bignoniaoeous 

 Bhrub with abuudance of dark blue flowers was also plentiful ; 

 while a white-flowered Liliaceous plant formed large patches 

 on the hillsides. Besides these there were two species of woody 

 Composite with conspicuous heads of yellow blossoms, and a 

 species of white-flowered Myrtle also' abundant; bo that, on 

 the whole, flowers formed a rather conspicuous feature in the 

 aspect of the vegetation 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 its dis- 

 tribution of insects and plants — is well explained by the exist- 

 ence of two species of humming birds in Juan Fernandez, 

 which in their visits to these large and ehowy flowers fertilise 

 them as effectually as bees, moths, or butterflies. 



This leads to the observation that many other groups of 

 birds also, no doubt, aid in the fertilisation 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 Artamus, or swallow-shrike, shot 

 at Cape York, showing that this genus also frequents flowers 

 and aids in their fertilisation. It must also be remembered, 

 as Mr. Moseley ha3 suggested to me, that a flower which had 

 acquired a brilliant colour to attract insects might, on trans- 

 ference to another country and becoming so modified 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 mo3t of the other plants of the island have colourless 

 flowers in accordance with the almost total absence of winged 

 insects. The researches of Dr. Herman Miiller have shown us 

 by what minute modifications of structure or of function many 

 flowers are adapted for pirtial insect and self fertilisation in 

 varying degrees, so that we have no difficulty in understand- 

 ing how, as the insects diminish and finally disappear, 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. 



As the sweet odours of flowers are known to act in com- 

 bination 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 ease, 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. 



PETROLEUM versos AMERICAN BLIGHT. 



Thanks for the information derived from a perusal of your 



Journal, I have been able to almost entirely get rid of that 



pest to my Apple trees, American blight. Last year the trees 



were completely covered, but after the fall of the leaf I had 



