20 



Oncidium varicosum, that grows in S. Brazil. This orchid throws 

 enormous flower spikes, and occasionally bears more than 200 

 flowers at a time, and the fertilising agent would have to become 

 very abundant indeed if every plant was to have even half its flowers 

 fertilised. Darwin records that Coryanthes triloba, a New Zealand 

 orchid with 200 flowers, only yielded five seed-capsules, "and at the 

 Cape of Good Hope only the same number were produced by 78 

 flowers of Disa grand/flora." It is quite possible that the energy 

 of these plants is insufficient to carry more than a relatively very 

 small number of seed pods, even if the amount of fertilisation was 

 on a very extensive scale. 



All orchids are bisexual except Catasetum, where the seeds are on 

 different plants, and all have a very complicated structure for fertili- 

 sation. Most of them are wonderfully adapted for cross-fertilisa- 

 tion, though it is possible to artificially cause self-fertilisation. In 

 the Vandece, which includes the vast majority of orchids, the structure 

 consists of stigma, rostellum and anther, all united into one. The 

 rostellum bears the pollen masses, which are removable, and when a 

 bee or other insect enters the flower for honey the viscid' portion at 

 the end of the pollen pedicil adheres to some portion of the bee's 

 body, or sometimes to the proboscis in the case of butterflies and 

 moths. The insect, flying off to another flower in search of more 

 honey, brings the pollen masses in contact with the externally viscid 

 and sensitive stigma and leaves the pollen behind to fertilise the 

 flower. On emerging from the same flower it removes other pollinia, 

 and the process is repeated. It should here be mentioned that it 

 has been found that if a flower is fertilised with the pollen of another 

 flower, yet has its own pollinia left in position, the flower is incapable 

 of producing a seed-pod, and the reason is probably this, that so 

 long as the pollinia are left in position the plant's energy is divided 

 between bearing a seed-pod and supporting its pollinia. As soon 

 as its own pollinia are removed the plant's whole energy goes to 

 forming a seed-pod. 



The fertilising structures in different orchids are so variable that it 

 is impossible here to touch on more than two or three in particular. 

 Those who have studied Darwin's "Fertilisation of Orchids" will 

 have appreciated the extraordinary amount of specialisation the 

 organs of reproduction in the Orchidacese have undergone. 



Orchids are divided into seven tribes : Malaxidece, Epidendrece, 

 Vandece, Ophrydece, Neottiece, Arethusece, and Cypripediece. Of these 

 Malaxidece, Ophrydece, A T eottiecc, Arethusecz and Cvpripediece are wholly 

 terrestrial or nearly so, and the Epidendrece and Vandece are 

 epiphytal. 



In the Ophrydece and the Neottiece are to be found the bulk of the 

 British orchids, but we have representatives of the Arethusece, 

 Malaxidece and Cypripediece. Orchis mascula of the Ophrydece is 

 well figured in Darwin's work and shows the structure most clearly. 

 The pollinium in this species consists of packets of pollen grains, 



