514 



ORDER NAIADE^E. GRASS-WRACK, POND-WEED. 



scope, the whole flower will come into view, having been pre- 

 viously hidden in a slit in the edge of the scale. The inflo- 

 rescence consists of a transparent membranous bag, having a split 

 on one side, through which the two stamens of the stamineous 

 flower pass out ; and within is also a pistilline flower with a 

 single-celled ovary, having a single style and stigma. The 

 sheath that incloses these is probably to be regarded as a large 



bract or spathe, like that 

 which will be particularly 

 described in the Arum tribe. 

 Such are the means by which 

 this little plant propagates 

 itself, which it sometimes 



does with amazing rapidity. 

 The Duckweed is so named, 

 from its being a favourite 

 article of food with water- 

 fowl. It is the only genus 

 PIO. 185.-A, SCALE OK DUCKWEED, with of its kind known in Europe ; 



flower a at its edge. B, THE FLOWER BEPA- and from itg sc i en tific name, 



Lemna, the group of which 



it may be considered as the type, is called LEMNACE.E. In tro- 

 pical countries, the surface of the water in ponds, tanks, &c., is 

 often covered with a sort of gigantic Duckweed, termed Pistia ; 

 this has acrid properties, with which it is said to impregnate the 

 water to such a degree, as to make it unwholesome. Neither 

 Lemna nor Pistia have spiral vessels ; so that in this respect 

 they might be associated with Cryptogamia. 



691. In the order NAIADES, we have almost as near an 

 approach towards flowerless plants; they are believed to be 

 equally destitute of true spiral vessels ; and they possess no dis- 

 tinct cuticle. In their general form and habits, many of them 

 strikingly resemble AlgEe ; from which, however, they are at 

 once distinguished when in flower. Of the British species, this 

 resemblance is the strongest in the Zostera marina, or Grass- 

 wrack, which is abundant on many parts of our coasts, and in 



