APPENDIX A 613 



the open entrance to the spur. It is the result of fusion of the single stamen 

 with the short style. 



The Androecium is represented only by a single anterior , fertile stamen, which, 

 owing to the resupination, faces the observer : each of its two purple 

 anther-lobes shows when ripe a longitudinal slit of dehiscence. The down- 

 ward-directed, but really apical end of the anther is covered by the small 

 globular rosiellum, which obstructs the entrance to the spur (Fig. 460, 1. 11.). 



The Gynoecium consists of three carpels, syncarpous and inferior. Of the 

 three stigmas one which is not receptive is represented by the rostellum (r), 

 the other two are merged into a hollow oval stigmatic surface (5) situated 

 below the rostellum. A transverse section of the ovary, preferably of a 

 flower already fertilised, shows a single cavity, with three parietal placentas, 

 and very numerous minute ovules. 



The Fruit matures as a dry capsule, splitting by six longitudinal slits into 

 three larger and three smaller strips, which remain united at their ends. 

 The minute seeds are scattered by the wind. 



Pollination. The flower being resupinate, the large posterior labellum pro- 

 jects forward as a convenient platform for the visiting insect, while the entry 

 to the spur is presented directly to his proboscis just below the column. 

 But the passage is obstructed by the rostellum. On inserting his proboscis 

 this is pushed aside. As it breaks away it lays bare two sticky discs, which 

 adhere to his proboscis, their cement setting firmly in the few seconds during 

 which he is engaged in probing the honey-containing tissue at the base of the 

 spur. On his withdrawing it, the coherent contents of the two anther-lobes 

 are themselves withdrawn, and appear as club-shaped pollinia, fixed by their 

 sticky discs in an erect position. But in a few seconds this position changes, 

 and they curve strongly forwards (Fig., 460, v. vi.). Meanwhile, if he has flown 

 to another flower, they are in such a position that as he inserts his proboscis, 

 they will impinge directly on its stigma, which is below the rostellum. The 

 pollen, which is in coherent masses, is then held by the sticky stigma. Thus 

 cross -pollination is effected with a high degree of certainty, while self-pollina- 

 tion is mechanically impossible. The efficiency of the mechanism is shown 

 by the constancy with which the Spotted Orchis sets its fruit as it grows in 

 the open. This is only one of the very various methods of pollination seen 

 in this wonderful family. For further details reference may be made to 

 Darwin's Fertilisation of Orchids. 



The Orchidaceae are a very large family, chiefly tropical, and often epiphytic, 

 though represented in the British Flora by many ground-growing species. 

 Their interest is chiefly biological and spectacular. One of the few useful 

 products is Vanilla, the dried fruit of an American climber. 



ORDER : GLUM ALES. 



The Cyperaceae and Gramineae, which are grouped under this heading, 

 have in common hypogynous flowers, more or less specialised in relation to 

 pollination by the wind, while their flowers are often grouped in dense in- 

 florescences. The Juncaceae may be associated with them as a Liliifloral type 

 only slightly modified. The construction of their flowers may be referred in 

 origin to the Liliaceous type, but the perianth is inconspicuous, and the 



