48$ THE DUCKWEED FAMILY. 



but anomalous in its mode of vegetation and very reduced 

 flowers. 



I. DUCK^VEED. LEMNA. 



Floating plants, without distinct steins or real leaves, but consisting of 

 small, leaf-like fronds, either separate or cohering two or three together by 

 their edges, emitting one or more fibres from their under sm-face into the 

 water, and multiplying by similar fronds growing out of their edges. Flowers 

 very rare, appearing from a fissure in the edge of the frond, and consisting 

 of a mmute membranous bract or spatha, enclosing 2 stamens (or 1 only in 

 an exotic species) and a single 1-celled ovaiy, vrith one or more ovules, a 

 short style, and no perianth. 



A small genus, mdely distributed over Europe, northern Asia, and North 

 America, but rare in the tropics. 



Roots in clusters. Fronds above 3 lines diameter 4. Greater D. 



Roots solitary. 

 Fiouds very thin, oblong or narrowed at one end (the young ones 



usually projecting on each side at right angles) 1. Ivy-leaved D. 



Fronds broadly ovate, under 3 lines diameter. 



Fronds rather thick, slightly convex underneath 2. Lesser T). 



Fronds very thick and convex underneath 3. Gibbous D, 



1. Ivy-leaved Duck^reed. Xiemna trisulca, Lin n . 

 (Eng. Bot. t. 926.) 

 Fronds very differently shaped from those of the other species, and much 

 thiuner. They are usually near 6 Unes long and about half that breadth, 

 thin, narrow and minutely toothed at one end, and ending ia a Uttle stalk 

 at the other, with 2 yotuig ones usually growing from opposite sides near 

 the base, and a smgle root from underneath. Flowers of the lesser D. 



On ponds and still waters. One of the common species on the Continent, 

 but less so ill Britain, especially in the north. Fl. summer, hut very rarely. 



2. Iiesser Duck^veed. Xaemna minor, Linn. 



(Eng. Bot. t. 1095.) 



Fronds usually about 2 fines 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 stUl waters, throughout the range of the genus, and gene- 

 rally tlie commonest species, often covering the water to a great extent, 

 Fl. summer, and more easily met with in that state than any other species, 



3. Gibbous Duckiveed. Iiemna gibba, Linn. 



(Eng. Bot. t. 1233.) 



Fronds shaped like those of the lesser J)., 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 the lesser D. it is everywhere less common. 

 Rare ia England and Ireland, and still more so in Scotland. Fl. summer, 

 very rarely. 



4. Greater Duck'weed. Iiemna polyrrhiza, Linn. 

 (Eng. Bot. t. 2458.) 

 Fronds larger than in any other species, attaining 3 or 4 lines diameter, 



