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422 THE DUCKWEED FAMILY. [Lemna. 



Fronds broadly ovate, under 3 lines diameter. 



Fronds rather thick, slightly convex underneath . 2. L. minor. 

 Fronds very thick and convex underneath . . . . 3. L. gibba. 

 Roots none. Fronds minute, with the flowera on the upper sur- 

 face 6. L. arrhiza. 



1. L. trisulca, Linn. (fig. 946). Ivy-leaved D. Fronds very dif- 

 ferently shaped from those of the other species, and much thinner. 

 They are usually near 6 lines long and about half that breadth, 

 thin, narrow, and minutely toothed at one end, and ending in a 

 little stalk at the other, with 2 young ones usually growing from 

 opposite sides near the base, and a single root from underneath. 

 Flowers of L. minor. 



On ponds and still waters. One of the common species on the Con- 

 tinent, but less so in Britain, especially in the north. Fl. summer, but 

 very rarely. 



2. L. minor, Linn. (fig. 947). Lesser D. Fronds usually about 2 

 lines long, broadly ovate or orbicular, cohering 3 or 4 together, with 

 1 root under each but without any stalk, quite ^entire, and of a rather 

 thick consistence. Ovary with a single ovule. 



On ponds and still waters, throughout the range of the genus, and 

 generally the commonest species, often covering the water to a great 

 extent. Fl. summer, commencing early, and more found in that state than 

 any other species. [The flowering patches may be discerned by their 

 yellowish hue.] 



3. L. gibba, Linn. (fig. 948). Gibbous D Fronds shaped like those 

 of L. minor, but rather larger and much thicker, flat above, spongy, and 

 almost hemispherical underneath, with a single root to each. Stamens 

 2. Ovary with 2 or more ovules. 



With the station and range of L. minor it is everywhere less common. 

 Local in England and Ireland, and rare in Scotland. FL summer, very 

 rarely. 



4. L. polyrrhiza, Linn. (fig. 949). Greater D. Fronds larger than 

 in any other species, attaining 3 or 4 lines diameter, broadly ovate or 

 orbicular, rather thick, with a cluster of roots under each one. Flowers 

 of L. gibba. 



As widely dispersed as the other species, and rather more frequent 

 than L. gibba, except in Scotland. The flowers have never been observed 

 in Britain. 



5. L. arrhiza, Linn. (fig. 950). Rootless D. Fronds rather thick 

 and swollen on the underside, but much smaller than in any other 

 British species, only half a line long and rarely emitting any root. 

 Anther solitary, globose, sessile. Ovary with a single ovule, the flower 

 and fruit issuing from the upper surface, not from the edge of the 

 frond as in the other species, on which account this one has been 

 separated as a genus under the name of Wolffia. 



On ponds and still waters, common in the warmer regions of Asia 

 and Africa, and perhaps in South America, more rare in Europe. 

 In Britain flowerless, and confined to the south-eastern counties. 

 Fl. summer. 



