typha LKMNACE.E 669 



LEMNA 



uppermost. Ovaries long-stipitate, 1 -celled, surrounded by num- 

 erous bristles and clavate rudimentary ovaries. Styles filiform. 

 Fruit nut-like, small, usually splitting on one side. Seeds linear 

 striate. 



T. latifolia L. Sp. 971. Stems stout, 4-8 feet high: leaves nearly 

 equalling or exceeding the stem, 3-12 lines wide: pistillate spike dark 

 brown or black, at length an inch in diameter; the staminate portion usu- 

 ally contiguous, each 3-12 inches long: pollen grains in 4's: pistillate 

 flowers without bracts : stigmas rhomboid or spatulate. In marshes 

 throughout North America, Europe and Asia, except the extreme north. 



T. angustifolia L. Sp. 971. Stems slender, 2-10 feet high ; leaves 2-6 

 lines wide, somewhat convex on the back: spikes light brown, the stamin- 

 ate and pistillate portions usually distant, the two together sometimes 15 

 inches long, the pistillate portion when mature 2-8 lines in diameter and 

 provided with bractlets: pollen grains simple: stigmas linear or linear-ob- 

 long. In marshes, California and Oregon to the Eastern States and Europe. 



Order CII LEMNACE^ Dumort. PL Belg. 147. (1827.) 



Very small floating stemless herbaceous plants consisting of 

 flattened disk-like fronds with one or more rootlets from the 

 middle below, and monoecious flowers without perianth imbeds 

 ded in the frond. Flowers consisting of 1-2 stamens or a flask- 

 shaped 1- celled several-ovuled pistil. Style simple, with fun- 

 nelform stigma. Fruit a 1-6-seeded utricle. Seeds compara- 

 tively large, with straight axile embryo, albuminous. 



1 Lemna Frond 1-5-nerved, with a single rootlet. 



2 Spirodela Frond 7-11-nerved, with several rootlets. 



1 LEMNA L. Sp. 970. 



Fronds 1-o-nerved, containing numerous aoicular raphides, 

 destitute of vascular tissue proliferous from a lateral slit, usually 

 on each side near the base, with a single rootlet. Flowers mar- 

 ginal, bracteate, diandrous. Filaments slender: anthers didymous, 

 each cell bilocular by a transverse partition, dehiscing transverse- 

 ly. Seeds 1-6, mostly ribbed. 



L. trisulca L. Sp. 970. Fronds thin, oblong or oblanceolate, 6-9 lines 

 long, attenuate at base into a slender stalk, very obscurely 3-nerved, often 

 without rootlets, usually several series of offshoots remaining connected: 

 bracts sac-like: seeds ovate, amphitropous, with small round operculum. 

 In ponds, throughout most of North America : also in Europe and Asia. 



L. minor L. Sp. 970. Fronds round to elliptic-ovate, 1-3 lines in di- 

 ameter, rather thick, very obscurely 3-nerved: seeds oblong-obovate. 

 amphitropous, with prominent rounded operculum. Common in ponds in 

 all parts of the world. 



2 SPIRODELA Schleiden Linn. xiii. 391. (1839.) 



Fronds 7--12-nerved. Rootlets several, with axile vascular 

 tisue. Anther-cells bilocellate by a vertical partition and longi- 

 tudinally dehiscent. Ovary 2-ovuled. 



S. polyrhiza Schleiden 1. c. Fronds round-obovate, 2-5 lines long, 

 thick, flat and dark green above, slightly convex and purple beneath, pal- 



