272 FLORA OF TEXAS. 



MYRIOPHYLLUM, Vail. Water-Millfoil. 



Flowers monoecious or polygamous; calyx 4-parted in 

 the sterile flowers, 4-toothed in the fertile ones ; petals 4 or 

 none; stamens 4 or 8; stigmas 4, recurved; /n<?Y bony, 

 4-celled, 4-lobed, indehiscent. — Aquatic perennial herbs, 

 with the submerged leaves pinnately divided into filiform 

 or capillary segments, and commonly whorled; flowers 

 minute in the axils of the upper leaves, the uppermost 

 sterile. 



* stamens 8 ,• fruit even or warty. 



M. LAXUM, Shuttl. Stem long, slender; leaves 4 in a 

 whorl, the floral ones reduced to minute nearly entire 

 spatulate bracts, shorter than the flowers, which thus form 

 an interrupted almost naked spike ; fruit roughened with 

 minute warts, with the lobes obtuse. Ponds and lakes. 



M. VERTiciLLATUM, L. Leaves in whorls of 3-4, the 

 floral ones linear, pectinately toothed, much longer than 

 the flowers ; fruit smooth. Still water. Stem 2°-4° long, 

 stouter than the last. 



** stamens 4 ; fruit ridged and roughened. 



M. HETEROPHYLLUM, Michx. Stem thick ; leaves 4-6 in 

 a whorl, the floral ones crowded, ovate or lanceolate, finely 

 and sharply serrate; the lower ones pinnatifid; fruit 

 slightly roughened. 



49. CACTUS FAMILY. Order, Cactace^. 



Succulent, shrubby, and commonly leafless and prickly 

 plants, with globular, or columnar and angular, or flat- 

 tened and jointed sterns, and solitary sessile floivers; sepals 

 and petals similar, imbricated in several rows, and ad- 

 herent to the 1-celled ovary; stamens indefinite, with long 



