494 PART IV. -CLASSIFICATION. 



the <? and ? inflorescences occur on the same axis. In one large section 

 of them the two kinds of flowers occur on the same spike which is either 

 <? at the base and ? at the top, or vice versa. When this is the case the 

 axis bears either only one terminal spike, as in Carex pulicaris and C. 

 pauciflora, or several spikes forming a capitulum at the apex, as in C. 

 cyperoides, or a spike or a panicle, as in C. muricata, arenaria, and panicu- 

 lata. In a second section, on the other hand, each spike is unisexual, and 

 then the <J spike is almost always terminal on the axis and the ? lateral, 

 as in Carex acuta, glauca, prcecox, digitata, flava, and paludosa. 



SUB-CLASS III. PETALOIDE^. 



Flowers rarely unisexual ; perianth rarely wanting, usually 

 biseriate, the corolla usually petaloid, and sometimes the calyx also. 



SEEIES I. HYPOGYN.E. 



Ovary superior. 



Sub-series. Apocarpce. 



Gynseceum more or less completely apocarpous. 



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

 quently unisexual ; seeds without endosperm. 



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

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

 Water-plants. 



In the genus Naias the flowers are solitary or in spikes, and are either 

 monoecious or dioecious: perianth of one or two gamophyllous series: $ 

 flowers with 1 stamen, ? flowers with one carpel : ovule erect. N. flexilis 

 is the only British species. In Zostera, the Grass-wrack, the flowers are 

 diclinous, 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 waters of estuaries. In Zannichellia, 

 the Horned Pondweed, the flowers are diclinous, and are solitary or in 

 spikes: S flower, perianth 0, stamen 1; V flower, perianth bell-shaped, 

 carpels 4-6. Z. palustris is the only British species. 



In Potamogeton, the Pondweed, the flowers are monoclinous and in 

 spikes: general formula PO, A2 + A2, G x 4 : the extrorse stamens have a 

 broad leafy connective. This genus is represented in Britain by many 

 species : in some (.P. pusillus) the stem bears only submerged leaves which 

 are narrow and linear ; in others the leaves are somewhat broader (P. 

 densus), and in others again it bears a few broad leaves which float on the 

 water (P. natans). In Ruppia, the Tassel Pondweed, the flowers are gener- 



