524 BOTANY PART ij 



pous, in JJutomus G 3 + 3, in Alisma G oo . SagMaria is mnmccious with 

 flowers tliat by suppression of stamens or carpels are unisexual. Male flowers, 

 with numerous stamens and sterile carpels ; female flowers, with staminodes and 

 numerous free carpels inserted on the convex floral- receptacle (Figs. 515, 516). 

 Leaves in Butcmius, linear, channelled, and triangular in cross-section ; in Alisma 

 and Sagittal-la, long - stalked, with spoon -'shaped and sagittate leaf -blades 

 Respectively. -Individuals of both genera growing in deep flowing water have 

 Jong ribbon - shaped leaves, similar to those that appear as a transition type 

 in germination : such plants do not flower. \ 



Family 2. Juncaginaceae. Habit grass-like, Triglochin. 



Family 3. Potamogetonaceae (Fig. 517). Many species of Fotamoyeton are dis- 

 tributed over the earth in standing or flowing water. Flowers hermaphrodite, 

 tetramerous. Gyna'eceum apocarpous. Inflorescence a spike. Leaves usually 

 submerged, with a long sheath, slit on one side, formed from the axillary stipules. 

 ]'. mitatis, the common Pond-weed, at the time of flowering has usually only float- 

 ing leaves, the cylindrical, submerged water-leaves having disappeared by then. 

 Ruppia maritima and Zanichdlia palustris grow in brackish water. Zostcm 

 marina. ( irass- wrack, occurs commonly on all north temperate coasts and is used for 

 stuffing cushions (cf. p. 307). 



Family 4. Naiadaceae. The single genus Naias contains a number of fresh- 

 water plants with diclinous flowers. 



Family 5. Hydrocharitaceae. Hydrocharis moi-sim runnr and Stratiotes aloidfs 

 are floating plants occurring in Britain, which are vegetatively propagated by 

 runners ; they pass the winter at the bottom of the water, in some cases as special 

 winter buds (cf. j>. 301), and grow up again in the spring. Flowers dioecious ; 

 perianth differentiated into calyx and corolla. The male flower has several 

 trimerous whorls of stamens ; the female flower possesses staminodes and two 

 trimerous whorls of carpels. Ovary inferior, entomophilous. Vallisncria spiralis 

 (cf. p. 307). Elodea canadensis, the Canadian water-weed. 



Order 2. Glumiflorse 



This order consists entirely of annual or perennial plants of grass- 

 like habit. A woody stem only appears in the genus Bambnsa. The 

 association in more or less complex inflorescences of numerous flowers, 

 which lack a proper perianth but are enclosed by scaly bracts (glumes), 

 is a common character of the order. The perianth is either completely 

 wanting or reduced to a series of scales or bristles. The inner whorl 

 of stamens is also wanting. The superior ovary is always unilocular 

 and contains only one ovule ; it is formed of three, two, or of a single 

 carpel. The large size and feathery and papillose form of the stigmas 

 stand in relation to the wind pollination. Fruits indehiscent. 



Family 1. Cyperaceae. The Sedges are characterised by their 

 triangular stems, which are usually neither swollen at the nodes nor 

 hollow, and by their closed leaf-sheaths. The flowers are unisexual 

 and usually moncecious or are hermaphrodite ; ovary formed of two 

 or \ three carpels with an erect, basal, anatropous ovule. Pericarp 

 not coherent with the seed-coat ; embryo small surrounded by the 

 endosperm. 



