ANGIOSPERM^, MONOCOTYLEDONES. 745 



united into a single abbreviated column. Endosperm is present in the seeds. The 

 tribe Pistem includes floating plants with leaves arranged in rosettes and propagat- 

 ing vegetatively by means of stolons. The Arecß, of which the Arum (figs. 421 ^' ^' ^) 

 may be taken as a type, have subterranean tuberous stems, from which arise the 

 leaves and spadices. Numerous representatives of other tribes, including Ariopais, 

 Caladium, Dracontium, and Amorphophallus have tubers. Atnorphophallus 

 titanum, the giant of this family, has a tuber 50 centimetres in diameter, and 

 produces umbrella-like leaves on stalks 2-5 metres long and with segments in 

 proportion. The inflorescence is a huge spadix some 2 metres high, encircled by 

 a sheath of beautiful mottled green with purple lining and frilled edge. When this 

 plant flowered at Kew in 1890 (for the first and as yet only time in captivity) it 

 was one of the sensations of a London season. It is a native of Sumatra. A few 

 species of Montrichardia (M. linifera) and Philodendrou (P. bi'pinnatifidnmi) 

 have erect cylindrical stems, whilst the Snake-root {Calla palustris) and Sweet 

 Flag {Acorus Calamus) have creeping rhizomes. Many tropical Aroids belonging 

 to the tribes Monsterese and Pothoideae climb up the stems of trees, fastening 

 themselves by their aerial roots, and pass from crown to crown like lianes. The 

 Himalayan Raphidophora decursiva (fig. 422) is an example of this type of growth. 

 Many of these climbing Aroids send down pendent aerial roots into the humid air 

 of the forest (fig. 423), and these not unfrequently reach the ground, take root, and 

 become stretched taut. 



The majority of Aroids are tropical, less than 10 per cent of the species being 

 met with in temperate regions. Acorus Calamus, Arum mactdatum, and Calla 

 palustris reach the furthest north. The curious Ariopsis peltata (fig. 421 ^) occurs 

 in the Himalayas to a height of 1600 metres. 



There are about 900 species of living Aroids. 



The Lemnacece is a little family of reduced forms allied to Aroidese. The 

 flowers are unisexual, and consist of a stamen and a carpel respectively. They are 

 floating, flattened forms, and include Lemna (the Duckweed), and Wolffui, which is 

 destitute of roots. 



Associated with the Spadicifloreae are the Pandanaceae, which include Pan- 

 danus utilis, the Screw Pine (c/. vol. i. fig. 186, p. 758); Cyclanthacea?, climb- 

 ing and palm-like ; Sparganiacete and Typhacese, marsh plants, which include 

 Sparganium, the Bur-reed, and Typha, the Bulrush. 



Alliance XXXIV.— Glumiflorae. 



Families : Graviinew and Cyperacece. 



This alliance, which includes some 6000 species, consists exclusively of Grasses 

 and Sedges, forms with insignificant flowers destitute of coloured perianths and 

 pollinated by wind. 



Graminece. — Annual and perennial plants with upright, jointed haulms, and in 

 the case of perennials, provided with creeping rhizomes. The leaves consist of an 



