118 CACTACEiE. 



2. M. VERTICILLATUxM, L. Whorled Water Milfoil 



Leaves Ycrtieellate pinnately divided into capillary or setaceous segments ; floral 

 leaves pectinate pinnatifid, usually longer than the flowers; petals oblong-oborate ; 

 tarpels smooth and even. 



In water. July— Sept. Stem long and stouter than in the preceding, only th© 

 upper part cm> rging. Flowers small, green, in a terminal spike with conspicuous 

 floral leavi s. 



3. M. heterophyllum, Michx. Various-leaved Wuter 

 Milfoil 



St m rt.thcr stout; floral leaves ovate and lanceolate, thick, crowded, sharply 

 ••rrate; *ower leaves pinnatifid ; petals oblong; fruit obscurely roughened. 



In elucgish water. July. Stem thick and branching. Leaves very various, 

 lowest fit cly divided. Flowers purple, whorled in the axils of the upper leaves. 

 Sepds minute. I\taU somewhat persistent. Stamens sometimes only 4 to t>. 



* * Sto.me7is 4; leaves whorled in fours and flies, the lower find y divided. 



4. M. AMBIGUUM, Ambiguous Water Milfoil 



' Sulm>rseol leaves cut into capillary segments; the emersed ones pectinate ; floral 

 ones linear, tapering into a short petiole, toothed or entire; flowers mostly perfect ; 

 petals ollong; carpels smooth and even. 



Ponds and ditches. July, Aug. Stems 2 to 6 inches long and creeping in th« 

 mud, or when floating in water, long and slender. Leaves variously divided, when 

 the sten s are procumbent and rooting the leaves are all linear, rigid, and often 

 entire, but when submersed they are finely divided like the teeth of a comb. 

 FUavus small purplish. 



HIPPURIS. Linn. Mare's-tail. 



Gr. hippus, a horse, and euro, a tail. 



Calyx entire. Petals none. Stamen 1, inserted on 

 the edge of the calyx. Style single, thread-shaped, stig- 

 matic down one side, received in the groove between the lobes 

 of the anther. Fruit nut-like, 1-celled, 1-seeded. — Peren- 

 nial aquatics with simple entire leaves in whorls, and minute 

 flower* sessile in the axils, perfect or polygamous. 



H. VULGARIS, L. Common Mares-tail 



Leaves in whorls of 8 to 12, linear, acute, smooth, entire. 



Borders of ponds and springs; rare. Stem 12 to IS inches high, simple, erect. 

 Flowers at the base of the upper whorls, one to each leaf, sma!'. 



Order 44. CACTACE2E. Cactus Family. 



Fleshy and thickened leafless plants of peculiar aspect, globular or columnar and 

 inany-anghd or flattened and Jointed, usually with pric\ies. Flowers seditary, ses&ilt; 

 pie itpo.ls end petals numerous, imlricated in several rows. Stamens numerous, 

 with long end slender filaments, inserted on the inside of the tube or cup formed 

 by the union of the sepals and petals. Style J, Stigmas numerous. Feu? a 

 1-celled succulent berry, many -seeded. 



