ORCHIS FAMILY. 403 



* * Floating, spreading by proliferous shoots;- leaves long petioled, rounded heart- 

 shaped. 



8. LIMNOBIUM. Flowers monoecious or diu'cious, from sessile or short-stalked leaf-like 

 spathes, the sterile spathe of one leaf surrounding 3 long-pediceled staminate flowers ; 

 the fertile 2-leaved, with one short-pediceled flower. Perianth of 3 outer oval lobes 

 (calyx) and 8 narrow inner ones (petals). A cluster of 6-12 unequal monadelphous 

 stamens in the sterile flower ; some awl-shaped rudiments of stamens and a 6-9-celled 

 ovary in the fertile flower; stigmas 6-9, each 2-parted. Fruit berry-like, many- 

 seeded. 



1. ELODEA (or ANACHARIS), WATER WEED. (Greek: marshy?) 

 Flowers summer. 2/ 



E. Canadensis, Michx. Slow streams and ponds ; a rather homely 

 weed, with long branching stems, beset with pairs or whorls of pellucid 

 and veinless, 1-neryed, minutely serrulate, sessile leaves ($'-!' long), 

 varying from linear to ovate-oblong, the thread-like tube of the yellowish 

 perianth often several inches long. 



2. VALLISNERIA, TAPE GRASS, EELGRASS of fresh water. 

 (Named for A. Vallisneri, an early Italian botanist.) Flowers late 

 summer. 11 



V. spiralis, Linn. In clear ponds and slow streams, with bright green 

 and grass-like linear leaves (l-2 long), delicately nerved and netted; 

 fertile scapes rising 2-4 long, according to the depth of the water, after- 

 wards coiling up spirally and drawing the fruit under water to ripen. 

 The leaves of this and the preceding are excellent to show cyclosis. 



3. LIMNOBIUM, FROGBIT. (Greek: living in pools.} Flowers 

 whitish, the fertile ones larger, in summer. 2/ 



L. Sp6ngia, Richard. Floating free on still water, N. J., W. and S. ; 

 rooting copiously ; leaves l'-2' long, purple beneath, tumid at base, with 

 spongy air cells. 



CXII. OKCHIDACEJE, ORCHIS FAMILY. 



Herbs, with perfect flowers of peculiar structure, the perianth 

 adherent to the 1-celled ovary (which has numberless minute 

 ovules on 3 parietal placentae), its chiefly corolla-like 6 parts 

 irregular, 3 in an outer set answering to sepals, 3 within and 

 alternate with these answering to petals, one of these, generally 

 larger and always different from the others, called the labellum 

 or lip ; the 1 or 2 stamens are gynandrous, being borne on or 

 connected with the style or stigma (Lessons, Fig. 284) ; the 

 pollen is mostly coherent in masses of peculiar appearance, 

 celled pollinia (Lessons, Figs. 320, 321, 322). All perennials, 

 and all depend more or less upon insects for fertilization. 

 Beginners will not very easily comprehend the remarkable 

 structure of most Orchideous flowers. There are numerous 



