94 CABOMBACE.E. 



the seed, except the hilar extremity, where it is depressed to 

 make room for the lenticular sac {vitellus, sac of the amnios) 

 which incloses the embryo, perforated by a central canal 

 (the vestige of the extension of the sac in the ovule to the 

 chalaza). Embryo small, lenticular, conformed to the sac, 

 which it fills : radicle nearly obsolete, superior : the coty- 

 ledons very thick and fleshy, much thicker than long, in- 

 closing an oblong fleshy plumule. 



Herbs growing in ponds and slow streams, with slender 

 stems, furnished under water with chiefly opposite palmately 

 or peltately and filiformly many-parted leaves ; the upper- 

 most leaves floating, entire or emarginate, centrally peltate 

 on long petioles. Flowers solitary on long axillary pedun- 

 cles, white or yellowish. 



Etymology. Apparently an aboriginal name. 



Geographical Distribution. There are two species in Brazil anil 

 Guiana, and one in the Southern United States. 



PLATE 38. Cabomba Caroliniana, Gray; — summit, of the natural size. 



1. A flower, enlarged. 



2. A sepal, enlarged. 



3. A petal, equally enlarged ; inside view. 



4. A magnified stamen ; seen from the outside. 



5. Same, seen from the inner side. 



6. The pistils, magnified. 



7. A magnified pistil, the ovary divided longitudinally. 



8. Fruiting pistil, with an infertile one ; enlarged. 



9. A magnified seed, with the hilar operculum, 10, detached. 



11. Vertical section of the same, showing the embryonic sac at the extrem- 



ity of the albumen. 



12. A portion (the hilar end) of the same section, more magnified (and re- 



versed), displaying the embryo, surrounded by the sac, which is 

 seen in section, at the base of the albumen. 



13. The embryo, detached, with the cotyledons separated, to show the 



plumule. 



