484 BOTANY 



the systematic position of the Potamogetonaceae is difficult to determine. The 

 family consists of water-plants whose leaves are usually narrow and submerged, 

 while the inflorescences sometimes rise above the surface of the water, sometimes 

 remain continually submerged. The flowers, always small and inconspicuous, are 

 pollinated by the wind or water. The members of this family constitute a chief 

 part of the fresh - water flora of all zones. Potamogeton, Pond - weed, and 

 Zannichellia, Horned Pond-weed, are familiar fresh-water genera. Some species 

 are found in salt water, where they cover extended areas in the neighbourhood of 

 the coast with a submerged vegetation, e.g. Zostera marina, Grass-Wrack or Eel- 

 grass, found in salt water throughout all zones. It is used for stuffing cushions, 

 etc. , and is the only plant of economic value in the whole order. 



The small family Najadaceae (flowers diclinous, one stamen, one ovary) is 

 closely related to the preceding, which it resembles in appearance and habit. 

 Najas major may serve as an example. 



The Triwidaceae are a small tropical family of terrestrial plants, all of which 

 are saprophytes and devoid of chlorophyll. In structure their flowers resemble 

 those of the A lismaceae. 



Order 6. Scitamineae 



Flowers epigynous, zygomorphic or asymmetrical ; androecium 

 reduced, often partly petaloid ; ovary usually trilocular ; seeds 

 with perisperm. 



The Scitamineae are herbs, usually with perennial rhizomes and 

 with large pinnately-veined leaves, which may be narrow or elliptical. 

 The flowers are adapted to insect-pollination ; the perianth is 

 in some cases differentiated into a calyx and corolla, or developed 

 as a corollaceous perigone. The structure of the androecium is 

 especially characteristic. Although in certain cases (e.g. in the 

 flowers of the Banana) it differs from the regular type merely in the 

 absence or staminodial development of the posterior stamen, in the 

 majority of the Scitamineae only one fertile stamen is present. The 

 other members of the androecium are then either suppressed or they 

 assume the form of petaloid staminodia, which give the flowers a 

 distinctive shape and appearance (Figs. 429 C, 

 430). The fruit is variously developed and 

 furnishes no characteristic features. 



Family Musaceae. — Mowers zygomoephic, with 

 FIVE fertile stamens. Tropical herbs, arborescent in 

 appearance, rarely true trees, with enormously large 

 leaves. 



The Banana (Musa sapientum and Musa paradisiaca) 

 Pio. as.-Zingiberace ae. is largely cultivated in all tropical countries for the sake 

 Floral diagram (Zingiber). of its edible baccate fruit. 



Family Zingiberaeeae. — Flowers zygomorphic; the posterior 



STAMEN OF THE INNER WHORL ALONE FERTILE, AND THE TWO 



LATERAL, inner stamens connate and transformed into a 



