APPENDIX 



is capricious and not of frequent occurrence, while, as I have said more 

 than once, their flowers are often high up on the trees, beyond reach. 

 With the exception of Birtbophyllum Beccarii, which attracted flies, I 

 have personally never seen in Borneo an orchid in flower on which a 

 butterfly or any other insect was posed. Probably some of the insects 

 which visit the flowers are nocturnal or crepuscular, which is another 

 obstacle to observations on the interdependence of insects and the 

 flowers which they frequent. 



If the flowering of orchids is infrequent and capricious, as a com- 

 pensation their blossoms in most instances last a long while, which is 

 in itself a proof of the difficulties which beset their fertilisation. The 

 flowers last long because they have to wait long for an opportunity of 

 fecundation, and this circumstance tends to show, that for some cause or 

 other insects are not naturally too prone to visit them. Many orchids 

 under natural conditions hardly bring to maturity a single fruit of the many 

 they bear. And this difficulty and the long delay in fecundation may 

 account for the surprising mechanisms which the flowers reveal in their 

 reproductive organs. It appears to me to be almost a general rule that 

 the more a plant is provided with anomalous, complicated, and uncommon 

 contrivances, the more precarious and difficult must have been its con- 

 ditions of existence in past evolutive periods. It is a fact that plants 

 so provided are rare and localised. They have been, as it were, dis- 

 satisfied with their position, and have endeavoured to better it by special 

 adaptations, but the complications attending these have finally proved 

 a disadvantage rather than an advantage to them. 



Passing now to the forms of Bornean orchids, it is worthy of note that, 

 both in their foliage and their stems, these show a remarkable polymor- 

 phism, exhibiting all the ways and means known proper to epiphytes 

 to enable them to live in the peculiar physical conditions which they have 

 chosen. 



Although various terrestrial orchids are found in Borneo, none, as 

 far as I am aware, are provided with underground tubers, a character 

 which appears to be peculiar to members of the family living in localities 

 where terrestrial vegetation has alternate periods of activity and rest. 

 Many of the epiphytal orchids of Borneo, however, possess basal enlarge- 

 ments, which may be looked upon as aerial bulbs, for the plants find on 

 the branch of the tree on which they grow that marked diversity in the 

 conditions of alimentation, absorption, and assimilation between the 

 inferior part of the stem and the leaves, that bulbous plants find in the 

 soil — a diversity of conditions which may indeed have been the first 

 origin of bulbous plants. Amongst all the various structural forms in 

 the vegetative parts of the Bornean orchids, there is one which has 

 specially surprised me — the rush-like form which is assumed by some 

 few, for it corresponds to a type frequent in marsh-loving plants. It 

 would be interesting to know what is the physiological connexion existing 

 between plants which live in localities where water abounds, and these 

 xerophil epiphytes, which have to battle with drought. This analogy 

 of existence between epiphytal and paludal plants exists also between 

 the various species of Nepenthes, some of which are epiphytes, while 

 others are aquatic. 



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