GttOUP IV. PHANEROGAMIA : A.NGIOSPERM^ : MONOCOTYLEDONES. 553 



SUB-CLASS III. PETALOIDE^E. 



Flowers ambisporangiate, rarely nionosporangiate ; perianth 

 rarely wanting, usually biseriate, the corolla usually petal old, and 

 sometimes the calyx also. 



SERIES I. HYPOGYN/E. 



Ovary superior. 



Sub-series. Apocarpce. 



Gynseceum more or less completely apocarpous. 



Cohort 1. Alismales. Marsh- or water-plants ; flowers fre- 

 quently monosporangiate ; seeds without endosperm. 



Order 1. NAIADACEJ;. Perianth 0, or of 2-4 segments ; stamens 

 1-4 : ovaries 1-4, with usually a single erect or suspended ovule. 

 Water-plants. 



Fam. 1. Naiadece. Flowers monosporangiate. 



In the genius Naias the flowers are solitary or in spikes, and are dioecious: 

 perianth of one or two gamophyllous series : c flowers with 1 stamen, 9 flowers 

 with 1 carpel : ovule erect. N. ftexilis is the only British species. 



Fam. 2. Zostcrece. Flowers monosporangiate. 



In Zostera, the Grass-wrack, the flowers are monoecious, and without a 

 perianth ; they are borne in two rows on one side of a flattened spike ; stamen 

 1, carpel 1. Zostera marina and nana are the British species living in the 

 brackish water of estuaries. Phyllospadix, a North American (west-coast) genus, 

 also belongs to this family : it is dioecious. 



Fam. 3. Zamrichelliece. Flowers monosporangiate. 



In Zannichellia, the Horned Pondweed, the monosporangiate flowers are 

 monoecious, and are solitary or in spikes : $ flower, perianth 0, stamen 1 ; ? 

 flower, perianth bell-shaped, carpels 4-6. Z.palustris is the only British species. 

 Altheuia, the other genus, is sometimes dioecious. 



Fam. 4. Cyinodocece. Marine. Flowers mouosporangiate, dioecious : perianth 

 : (J flower consists of two connate stamens; flower of two adjacent mono- 

 inerous ovaries, each bearing a style which branches into two stigmata ; ovule 

 single, suspended, orthotropous. 



To this family belongs the genus Cymodocea (with the sub-genera Phu- 

 cagrostis, Physoschoenus, and Amphibolis) ; widely distributed on tropical and 

 sub-tropical sea-coasts. 



Fam. 5. Posidoniece. Marine. Flowers monosporangiate, sometimes , in 

 cylindrical compound spikes, the upper flowers of which are <$ : perianth : the 

 $ flower consists of 3 stamens, the $ flower of a single carpel. 



To this family belongs the siugle genus Posidonia ; P. oceanica inhabits the 

 shores of the Mediterranean. P. australi* the shores of temperate Australia. In 

 Zostera, Posidonia, and Cymodocea, the pollen is filiform or confervoid (see p. 520j. 



Fain. 6. Potainogetonetf. Flowers $ . 



