NOVEMBER. I I 



the orchids now coining into flower belong to the genus 

 Pterostijlis, so named from the winged style or column. 

 The plants have grass-like or broadish green leaves, and 

 the different species vary in height from 6 in. to 2 ft., but 

 each bears only one rather large green flower, which is 

 nearly quite closed up except in front. The peculiarity of 

 its structure is that the lip or labellum, which hangs just 

 at the opening in front of the flower, is sensitive at its 

 lower end, so that when an insect enters the flower and 

 touches the sensitive part, this lip moves back and shuts 

 the intruder into a little box, the back and sides of which 

 are formed by the winged column. The only mode of exit 

 is by walking up the column ; but to do this the insect has 

 to pass the stigma, the sticky rostellum, and then the 

 anthers, so that it emerges carrying the masses of pollen 

 with it, to deposit them on the stigma of the next flower 

 visited. The whole details of the structure can be read in 

 Darwin's "Fertilisation of Orchids." 



The pretty white and red-spotted Dendroblum, one of 

 our few epiphytic orchids, may be found in flower towards 

 the end of the month in a few localities down the west side 

 of the harbour. A favourite spot for it used to be by the 

 big rocks above Port Chalmers. 



Two other orchids which begin to flower in November 

 are chiefly interesting as illustrating degeneration. Praso- 

 p/itjllinn colensoi is a greenish brown-streaked form which 

 is nearly or quite self-fertile. I am not sure whether it 

 has any fragrance or not, but it certainly belongs to a 

 genus of which some of the Australian forms are very 

 fragrant. It grows commonly in open grassy ground. 

 But still more abundant is a slender erect species known 

 as Microtis porrifolia, which has one sheathing leaf on its 

 stem, and bears small green flowers arranged in a close 

 spike. This has become absolutely self-fertilised, and with 

 a powerful lens it is often possible to see the pollen grains 

 on the summit of the column putting out their tubes, so 

 that they grow directly out of the anther on to the stig- 

 matic surface. These plants are evidently descended from 

 species which were originally specialised in structure and 



