554 



PART HI. THE CLASSIFICATION OF PLANTS. 



In Potatnogeton, the Pondweed, the flowers are in spikes: general formula 

 PO, A2 + A2, Gxi: 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. densm), and in others again it bears a few 

 broad leaves which float on the water (P. nataiu). 



In Kuppia, the Tassel Pondweed, the flowers are generally two on a spike; 

 formula PO, A2, G4. R. maritima is the British species. 



Fam. 7. Aponogetnnece. Flowers $ , in spikes: perianth of 2 or Spetaloidleaves: 

 general floral formula P2-3, ^6, G'6, but sometimes (as in Apovogeton distachytis) 

 there may be six stamens and many carpels : ovules marginal, anatropous, either 

 numerous, or as few as three. 



This family includes the single genus Aponogeton, an aquatic plant inhabiting 

 the tropical and temperate regions of Asia, Africa, and Australia. 



A. (Ouvirantra) fenestmlis is remarkable for tlie peculiar structure of its 

 leaves (see p. 55). 



Order 2. JuNCAGiNACEiE, Flowers sometimes dioecious ; both 

 perianth- whorls are sepaloid and inconspicuous ; anthers extrorse; 

 carpels sometimes coherent ; the outer whorl of carpels is occasion- 

 ally abortive ; ovules 1-2, anatropous, embryo straight. 



Triglochin palustre, tbe Arrow-Grass, is common in marshes and on the 

 margin of pools : carpels coherent till mature. The flowers are disposed spirally 

 in a long loose spike without bracts. Scheuchzeria pulustris is rarer ; it occurs 

 in bogs ; the flowers are set in the axils of distichous bracts : carpels free. The 

 other genera are, Tetroncium, from the Straits of Magellan, with dioecious 

 flowers ; and Lilaea, from the mountains of North and South America, which is 

 polygamous, having <J , $ , and ^ flowers. 



Fio. 859.— Diagram of the Flower of 

 Trig lochia. 



Fig. 360.— Floral diagrams. A of 

 Butomus. B Of Aligma. 



Order 3. Alismace^e. Flowers sometimes monoecious ; floral 

 formula J£3, C3, ^3^ + or 3, or oo, (t3 + 3 or go : perianth hetero- 

 chlamydeous ; the sepals are often coherent at the base ; the petals 

 are white or violet ; anthers extrorse or introrse ; carpels sometimes 

 partially coherent ; ovules 1--3, campylotropous, embryo curved. 



Aluma Plantago (Water Plantain, Fig. 360 B), has the floral formula K3, C3, 

 A3'^ + 0, GQ or more; the numerous, monomerous, one-seeded ovaries are 



