Callitriche. CALLITRICHACEiE. 171 



Ponds and slow-flowing streams (except the var. terreslris). April - August. The first 

 variety is not common ; the others are frequent. Some botanists consider what are usually 

 regarded as the solitary perfect flowers in this genus, to consist of two closely approximated 

 flowers ; the sterile being next the stem, and the pistillate on the outside ; and this is perhaps 

 the proper view of their structure. 



Order XCV. PODOSTEMACE^. L. C.Rich. The River-weed Tribe. 



Flowers perfect, or by abortion diclinous, arising from a spathe. Calyx none, 

 or of 2 - several sepals. Stamens I, 2 or many, often monadelphous : antbers 

 2-celled. Ovary free, 2- (rarely 3-) celled, with numerous ovules attached to 

 a central fle.shy placenta : stigmas 2-3. Capsule ribbed, usually more or 

 less pedicellate, opening by 2 - 3 valves which fall away from the dissepiment. 

 Seeds numerous, without albnmen. Embryo straight ; the cotyledons plano- 

 convex. — Herbaceous aquatic plants, with alternate leaves, which are some- 

 times entire, but usually cut into numerous irregular capillary segments. 

 Flowers minute, axillary or terminal, sometimes solitary, at other times 

 aggregated, spiked or racemed. 



1. PODOSTEMUM. Michx. Ji 2. p. 164; Endl. gen. 1832. niVER-WEED. 



[ From the Greek, pous^ podos, a foot, and stcmon, a stamen ; the stamens being apparently raised on a footstalk, in 

 consequence of their filaments being united bt'low.] 



Spathe tubular, entire. Flower pedicellate. Calyx? consisting of two collateral scales. 

 Stamens 2 (rarely 3) : filaments united below : anthers 2-celled. Ovary 2-celled : styles 

 2, fleshy, stigmatose on the inside. Capsule 2-valved. — Aquatic plants growing on stones 

 in the bottom of shallow streams, with finely dissected leaves and solitary axillary flowers. 



1. PoDOSTEMUM CERATOPHYLLUM, Michx. (Plate XCVIII.) River-wecd. 



Leaves dichotomoiisly many-parted, the segments linear-setaceous ; filaments united above 

 the middle. — Michx. I. c. t. 44 ; Pursh,fl. 1. p. 3 ; Nutt. gen. 2. p. 202 ; Ell. sk. 2. p. 518; 

 Torr. compend. p. 332; Beck, hot. p. 124; Darlingt. Jl. Cest. p. 10. P. abrotanoides, 

 Nutt. in jour. acad. Phil 7. p. 105. Lacis ceratophylla, Bongard, gen. Lads revis. p. ID, 

 (ex mem. de I'acad. St. Petersb. 6 ser. torn. 3) ; Hook, in comp. hot. mag. 2. p. 23. t. 20. 



Perennial ? Whole plant coriaceous, and of an olive-green color. Root consisting of fleshy 



22* 



