412 



CABOMBACE^. 



[Hypogynous Exogens. 



. Order CXLIX. CABOMBACEiE.— Watershields. 



Cabombacea, Torrey and Gray, ]. 54. (1838). — Cabombese, Rich. Anal. Fi'. (1808); Endl. Gen. 

 clxxxvi.— PodophyllaceaeJHydropeltideae, DC. Syst. 2.36. (1821) ; Prodr. 1. 112. (1824) .— Hydro- 

 peltideae, Schleid. in Wiegm. Arch. 6. 230. 



Diagnosis. — NymxJlial Exogeiis^ with distinct carpels, abundant alhuraen, and no visible 



torus. 

 Aquatic plants, with floating peltate leaves. Flowers axillary, solitary, yellow, or 

 purple. Sepals 3 or 4, coloured inside. Petals 3 or 4, 

 alternate with the sepals. Stamens definite or indefinite, 

 h;v'pogj'nous, arising from an obscure torus ; anthers 

 linear, tm'ned inwards, continuous ^\ith the filament. Car- 

 pels 2 or more, terminated by a short style. Ovules 

 orthotropal, pendulous. Fruit indehiscent, tipped by the 

 hardened style. Seeds definite, pendvdous ; embryo 

 minute, two-lobed, inclosed m the fleshy sac of the amnios, 

 at the apex of the nucleus, and external to an abundant 

 fleshy albumen. 



There can be no doubt about the near relationship of 

 these plants to Waterlihes, with which they coiTespond 

 in having a minute embryo inclosed in a \'itellus, and from 

 which they only differ in having disunited carpels, and a 

 very small number of sutural o^^lles. From Waterbeans, 

 with which they correspond in their disunited carpels, they 

 are distinguished by their abundant albumen, minute em- 

 bryo, nearly total want of torus, and having more seeds 



than one in each carpel. 

 Theu' relationship to Po- 

 dophyls is much more 

 remote, nor can they be- 

 long to the same Alliance, 

 although they have been 

 combined with that Or- 

 der by De Candolle. 

 Richai'd, who regarded 

 Waterhlies as Monocoty- 

 ledons, referred these 

 plants also to that great 

 class ; but he misunder- 

 stood the structure of 

 their embryo, which has 

 been well illustrated by 

 Schleiden. Nuttall describes the young leaves and flowers, together with the other 

 parts exposed to the air, to be covered « with an inconspicuous flocculent pubescence, 

 immersed in a gelatinous substance." This Schleiden states to 

 be a remarkable state of the epidermis, which consists of a 

 very thick layer of well-defined insoluble gelatme, in which 

 the cells of the epidermis are introduced. — Wiegm. 5. 230. 

 The same author says, that not a trace of spiral vessels can be 

 found in any of the submersed parts. I find the stem to con- 

 sist of a mass of small cellular tissue surroimding 15 or 16 

 large au'-tubes, and some smaller ones, m the centre of which 

 is a pah' of woody bundles, crescent-shaped in theii- transverse 

 section, A\'ith the convexity du^ected inwards. These bundles 

 consist of thin- walled elongated tissue, in the middle of which 

 is a solitary tube of larger size, apparently also an air-tube, 

 for I can find no trace of spu'al structm'e in it. 



Fig. CCLXXXVIII. 



Fig. CCLXXXIX. 



Fig. CCLXXXVIII.— Cabomba aquatica. 1. the pistil and calyx ; 2. sections of the carpels (Turpin); 

 3. a section of its seed. — Schleiden. 

 Fig. CCLXXXIX.— Section of the stem of Hydiopeltis purpurea. 



