THE DUCKWEED TRIBE. 251 



appear to be abundantly sufficient, if we arc to judge 

 from the immense quantities which rise every year to 

 the surface of our ponds. In Europe we have no 

 other plant belonging to the same natural order ; but 

 in tropical countries its place is occupied by a plant 

 called Pistia, which is a sort of gigantic Duckweed, 

 with broad lobed leaves like some Lichens, and a 

 more hi"-hlv orsranized flower. 



With these examples of imperfect Monocotyledo- 

 nous plants, I must dismiss that part of the subject ; 

 in my next letter I shall introduce you to the more in- 

 teresting and important tribes which furnishes us with 

 bread. 



EXPLANATION OF PLATE XXL 



L The Bullrush Ttibe. — 1. A slioot of Branching Bur-reed 

 (Sparganium ramosum) ; a a heads of barren flowers ; b h heads of 

 fertile flowers. — 2. A barren flower; aa a sepals. — 3. A fertile flower. 

 — 4. An anther seen from the side. — .5. The same viewed from the 

 edge. — 6. A seed. — 7. The same divided perpendicularly, with the 

 embryo in one end of the albiunen. — 8. The embiyo extracted. 



IL The Arrow-grass Tribe. — 1. A flower-spike oi Marsh Ar- 

 row-grass (Triglochin palustre.) — 2. A flower; aa a sepals; b stigma. 

 — 3. A perpendicular section of one of the cells of the ovary; b stig- 

 ma. — 4. A scale of the calyx a; with the anther, b, hing in it. — 5. 

 An anther seen on the side by which it discharges its pollen. — 6. A 

 ripe fruit. — 7 . A perpendicular section of one of its cells, shewing 

 the manner in which the seed lies in it. — 8. An embryo; a the slit 

 through which the stem is finally protruded: b the radicle; c the 

 cotyledon. 



IIL The Duckweed Tribe. — I. Vl&nU o^ furrowed Duckweed 

 (Lemna trisulca) floating on water. — 2. A plant magnified, and in 

 flower at cr. — 3. A flower extracted from the sht in which it laid; a 

 the membranous bag. — 4. A fruit. — ij. A seed. 



