94 VALLISXERIACEAE. 



3. LIMNOBIUM L. C. Richard, Mem. Inst. Paris, 32: 66. pi. 8. iSn. 

 Aquatic, stoloniferous herbs, the leaves fascicled at the nodes, petioled, broad, cordate. 

 Flowers monoecious, white, arising from sessile or stipitate, 2-leaved, membranous spathes. 

 Perianth 6 parted, the segments petaloid, the 3 outer oblong-oval, the 3 inner oblong-linear. 

 Staminate flowers 2-4 in a spathe, long-peduncled, the stamens united in a column bearing 

 6-12 anthers at different heights, sometimes producing only 9-12 staminodia, the filaments 

 tipped with abortive anthers. Pistillate flowers sessile or short-peduncled with 3-6 vesti- 

 gial stamens; ovary 6-9-celled with as many central placentae; stigmas as many as the 

 cells, each 2-parted. Fruit a many-seeded berry. [ Greek referring to the aquatic habitat.] 



Three or four species, natives of America. 



i. Limnobium Spongia (Bosc. ) L. C. Rich- 

 ard. Frog's-bit. (Fig. 209.) 



Hydrocharis Spongia Bosc, Ann. Mus. Paris, 9 : 396. pi. 



jo, 1807. 

 Limnobium Spongia L. C. Richard, Mem. Inst. Paris, 



32:66. pi. 8. 1811. 



Hydrocharis cordifolia Nutt. Gen. 2 : 241. 1818. 

 Limnocharis Spongia I,. C. Richard ; Steud. Xomencl. 



Ed. 2, Part. 2, 45. 1841. 



Blades of the leaves orbicular or broadly ovate, cor- 

 date or reniform, faintly 5-7-nerved and cross-veined, 

 purplish and spongy beneath, io // -2 / broad, on peti- 

 oles I'-ic/ in length. Stolons rooting and sending 

 up flowers and leaves at the nodes ; peduncles of the 

 staminate flowers 3 / -4 / long, those of the pistillate 

 flowers stouter, i / -2 / long, nodding in fruit 



In shallow, stagnant water, Lake Ontario, to Florida, 

 west to Illinois, Missouri and Louisiana. July-Aug. 



Family 7. GRAMINEAE Juss. Gen. 28. 1789.* 



GRASS FAMILY. 



Annual or perennial herbs, of various habit, rarely shrubs or trees. Culms 

 (stems) generally hollow, but occasionally solid, the nodes closed. Leaves 

 sheathing, the sheaths usually split to the base on the side opposite the blade; a 

 scarious or cartilaginous ring, naked or hairy, rarely wanting, called the ligule, 

 is borne at the orifice of the sheath. Inflorescence spicate, racemose or panicu- 

 late, consisting of spikelets composed of two to many 2-ranked imbricated 

 bracts, called scales (glumes), the two lowest in the complete spikelet always 

 empty, one or both of these sometimes wanting. One or more of the upper scales, 

 except sometimes the terminal ones, contains in the axil a flower, which is usualh 7 

 enclosed by a bract-like awnless organ called the palet, placed opposite the scale 

 and with its back toward the axis (rachilla) of the spikelet, generally 2 -keeled; 

 sometimes the palet is present without the flower, and vice versa. Flowers per- 

 fect or staminate, sometimes monoecious or dioecious, subtended by 1-3 minute 

 hyaline scales called the lodicules. Stamens 1-6, usually 3. Anthers 2-celled, 

 versatile. Ovary i -celled, i-ovuled. Styles 1-3, commonly 2 and lateral. Stigmas 

 hairy or plumose. Fruit a seedlike grain (caryopsis). Endosperm starchy. 



About 3500 species, widely distributed throughout the world, growing in water and on all kinds 

 of soil. Those yielding food-grains are called cereals. The species are more numerous in tropical 

 countries, while the number of individuals is much greater in temperate regions, often forming ex- 

 tended areas of turf. The time of year noted is that of ripening seed. 



KEY TO THE TRIBES AND GENERA. 



A. Spikelets i or 2 flowered, when 2-flowered the upper fertile, lower staminate; rachilla arti- 

 culated below the scales or the subtending involucre, and not extending beyond the flow - 

 Spikelets not flatu-m-d laterally. 



Flowering scale and palet hyaline; none of the scales spiny. 



Spikeleta monoecious; staminate and pistillate in the same panicle. I. MAYDEAE. 

 Spikelets perfect, or one staminate or rudimentary, mostly silky. II. ANDROPOGOXEAE. 

 Flowering scale and palet membranous sn-ond scale spiny (in ours). III. ZOYSI \ 

 Flowt-ring scale and palet coriaceous or chartaceous; spikelets mostly glabrous, involucrate in 



Xos. 13 and IJ; scales 3 or 4. IV. I'AMCEAE. 



Spikelets flattened laterally, i -flowered; scales 2. V. ORYZEAE. 



*This family has been elaborated with the assistance of MR. GEO. V. NASH. 



