2II2 



A TEXTBOOK OF THEORETICAL BOTANY 



pollen and as the flowers mature this pollen remains attached only by the 

 top of the rostellum. 



An insect visiting the flower inevitably touches with its head the viscid 

 material at the top of the rostellum and as a result withdraws the pollinia 

 when it leaves the flower. 



Corallorhiza is a north temperate genus with about fifteen species. They 

 are all saprophytes with much-branched fleshy rhizomes, but unlike Neottia 

 develop no roots nor do they produce any scale leaves. In many respects 

 it resembles the monotypic Epipogium aphyllum which is also found rarely 

 in Britain. The flowers of C. trifida (Fig. 2051) are greenish-yellow in 

 colour with a white labellum and a throat dotted with dark red spots. It is 



Fig. 2051. — Corallorhiza trifida. A, Flower. B, Ovary, partially cut open, 

 bearing the column. Above, the anther showing the two pollinia and the 

 small rostellum, below which is the long, tongue-shaped nectary. (A after 

 Sozverby. B after Kmith.) 



pollinated by small insects which alight on the anterior part of the labellum 

 and creep in to sup the nectar secreted by its posterior part. In doing so, 

 they strike against the projecting rostellum and thereby remove the pollinia, 

 which remain attached to the upper side of the insect and are transferred to 

 another flower. 



The genus Cat t ley a (Fig. 2052) is well known to orchid-growers, for 

 many species are in cultivation and some are extremely beautiful. They are 

 natives of tropical America. The labellum in this genus encloses the column 

 but is not united to it. From its base a nectary runs down into the ovary. 

 Each anther contains a pair of waxy pollinia, each having a ribbon-like tail 

 formed from a bundle of highly elastic threads to which a number of pollen 

 tetrads are attached. The lips of these caudicles protrude from the anthers 

 which lie on the upper surface of the rostellum. The anther, however, is 



