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A TEXTBOOK OF THEORETICAL BOTANY 



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Fig. 2024. — Thisiuia aseroe. A, Flowering shoot arising from the rhizome. Bagnisia 

 episcopalis. B, Flowering plant. C, Plant in fruit, showing the lobed underground 

 rhizome. (From " Flora Malesiana ".) 



Orchidaceae 



The Orchidaceae are a very large family of remarkabJe plants, indeed it 

 is the largest family of the Angiospermae with about 7,500 species. Some 

 are typical herbaceous land plants, many are epiphytes, while others are 

 saprophytes. Those which live as epiphytes, as well as some of the land 

 forms, are adapted to xerophytic conditions and store up water in thickened 

 leaves, swollen internodes, pseudo-bulbs or in aerial roots. 



Epiphytic orchids are very common in the tropics where they develop 

 long aerial roots for the absorption of water while other roots serve as 

 anchorage organs and for the intake of mineral nutrients. The orchids of 

 temperate countries are nearly all terrestrial. 



A number of species occur in Britain and while a few are common and 

 widely distributed, many are extremely local in distribution and arc only 

 rarely met with. Among the common species we may mention the Early 

 Purple Orchid {Orchis masciila) (Fig. 2025), Spotted Orchid (O. fiichsii), 

 Marsh Orchid {O. praetermissa), Green-winged Orchid (O. morio) and Pyra- 



