"26 THE president's address. 



scales wMcK form a protecting coat. When the plant has died 

 down the portion beneath the ground does not completely perish, 

 but its dead remains cling round the new stem, forming a kind 

 of veil consisting of long strips of tissue the cell-walls of which 

 have numerous oblique pores. The whole forms a capillary 

 system which holds moisture for the supply of the rhizoids of 

 the new stem, and thus acts in a way similar to that of the 

 -surrounding sphagnum to our native sundews. 



I spoke of this climbing habit as a secondary adaptation, but 

 it is really a tertiary. The primary adaptation of the green 

 leaf is to form a flat surface for exposure to the air and sunlight. 

 Secondary adaptations are not infrequent, especially in con- 

 nection with the climbing and insect-eating habits ; here in these 

 Australian Droseras a third adaptation is superposed on the 

 other two. In the genus Nepenthes, the pitcher- plants of tropical 

 Asia, these three adaptations of the leaf are superposed along 

 the leaf-axis — first the assimilating portion, then a tendril-like 

 portion for climbing and at the extreme tip the elaborate 

 insect-trap. It is interesting to note that there is in Australia 

 a small genus of pitcher- plants, Cephalotus, in which the pitchers 

 are distinct from the foliage-leaves and are associated with 

 these at the ground-level. The climbing Nepenthes is eminently 

 adapted to its habitat ; the plants climb on the trees or bushes 

 growing by the sides of streams where insects are plentiful, the 

 pitchers being held invitingly into the air ; and we may assume 

 that the Australian climbing Droseras have during some period 

 of their history found that their survival in the struggle for 

 existence was rendered possible only by leaving the earth-floor 

 and climbing over surrounding herbage or shrubs to exploit 

 the upper regions of the air for their necessary nitrogenous food. 



Now may I refer to a very different case, in which form, 

 structure and analogy with a large series of allied forms suggest 

 an adaptation which has, however, ceased to exist. You are 

 familiar with our British orchids and the means by which they 

 ensure pollination by the agency of insects. But our native 

 Bee-orchis, while retaining a striking form and coloration, has 

 lapsed into the habit of self-pollination, the pollinia merely 

 falling from the anther-case on to the stigma beneath. Similar 

 instances have been noted, but they are rare in this large and 

 widespread family, containing more than 6,000 species distributed 



