1302 A TEXTBOOK OF THEORETICAL BOTANY 



uncommon in the jungle and bears remarkable inflorescences. The plants 

 are epiphytic climbing shrubs which produce two kinds of shoots, the one 

 producing clasping roots and the other forming vegetative branches bearing 

 sessile leaves and terminating in cymose umbels of flowers. In these inflores- 

 cences the central flowers are abortive and their bracts become transformed 

 into large-stalked, pocket-like nectaries which form a more or less radiating 

 cluster below the inflorescence. The fertile flowers form a circle above 

 these nectaries, each flower borne on a long, horizontal pedicel and facing 

 downwards. The flowers are hermaphrodite, and each consists of 4-5 

 sepals inside which is a fused corolla which is shed like a cap to disclose 

 a large group of stamens, united to one another and to the base of the 

 corolla. In the centre lies the unilocular ovary containing numerous ana- 

 tropous ovules and with a simple style. 



The flowers are protandrous and when mature both they and the 

 nectaries are brightly coloured. The whole inflorescence is therefore 

 attractive to Humming Birds and also to many types of insects. Some 

 Humming Birds probably sup the nectar directly, but various insectivorous 

 species also visit the flowers to catch the insects. Both types of birds alike 

 may cause pollination, for in their efforts to reach the central nectaries the 

 tops of their heads come into contact, either with the pendulous anthers or 

 the stigmas, according to the age of the flowers, and cross-pollination is 

 eflFected. 



Belt records an unnamed species of Marcgravia in which the nectaries 

 had developed close to the pedicels of the flowers, which were themselves 

 turned upwards so as to form a kind of fence around the nectaries. In this 

 type he pointed out that the birds visiting the flowers would have their 

 breasts, rather than their heads, dusted with pollen. 



The species of plants visited by small birds belong to many genera, 

 among which the following contain species which are more or less completely 

 ornithophilous: Antholysa, Malvaviscus, Protea, Phrygilanthus, Feijoa, 

 Strelitzia, Musa, Ravenala, Fuchsia, Salvia, Hibiscus, Erythrina, Bignonia, 

 Aloe, Kniphofia and Lobelia. 



How many of these and other cases of ornithophily are obligatory and 

 how many are simply facultative is not known, for the boundary line with 

 entomophily is not clear. Some of the larger moths could, and probably 

 do, function in many flowers, equally as well as the smallest birds. 



The whole question of pollination by birds has as yet been very incom- 

 pletely investigated. It seems probable that in the tropics a considerably 

 larger number of birds are concerned in this process than the records sug- 

 gest. It must be remembered that there is a superficial resemblance both 

 in form and in motion between some of the smaller Humming Birds and the 

 larger Hawk Moths. Indeed Bates records that occasionally he shot these 

 great moths in mistake for Humming Birds. Among the other birds 

 involved in pollination are the Honey Suckers. These birds are common in 

 South Africa and Madagascar and it has been reported that they are respon- 

 sible for the pollination of a large number of difl^erent plant species. 



