DUCKWEED. 301 



My specimens were gathered near Warwick. Dr. Murray 

 states that rice-paper is made from a Chinese species of Cala- 

 mus. The Chinese bring it in their junks from Formosa. The 

 pith is taken out and soaked in water, then sliced and pressed. 

 Refuse pieces are used in making artificial flowers, and the 

 sheets of six or ten inches in length are used for drawings of 

 Chinese costumes, flowers, landscapes, &c. 



The DUCKWEED order is the next in succession. They are 

 all minute floating plants, covering the surface of ponds and 

 stagnant ditches. They are often blamed for the unwholesome 

 odour which arises from the ponds where they flourish ; but 

 this is exceedingly unjust, for in reality they purify the air to 

 some extent, consuming a part of the noxious gas given forth 

 by the stagnant water. 



There are some ponds near Warwick where the Lesser and 

 Gibbous Duckweeds (Lemna minor and L. gibba), abound. 

 The former has very small leaves ; flat above and below, con- 

 nected in floating masses ; the latter has larger leaves, very- 

 thick, and egg-shaped underneath. 



The Greater Duckweed (L. polyrhiza), has oval leaves, which 

 are purple underneath. It is one of the scarcer species, but I 

 had the good fortune to fish some out of the ditch that partly 

 encircles Christ Church meadows, Oxford. 



The other rare species is the Ivy -leaved Duckweed (L. tri- 

 siilca). Its leaves are lobed, and have stalks to them. We 

 have specimens from near Bishopton in Durham. 



The great use of Duckweeds, besides somewhat purifying the 

 air, is to shelter insects, and thus provide both animal and 

 vegetable food for the ducks, which gobble up the weed so 

 greedily. The roots of .these tiny plants consist in simple 

 threads hanging from their leaves. The flowers are rarely 

 found; they proceed from the side of the leaf, and consist 

 in two stamens and one stigma. It is related of a celebrated 

 botanist that his chief desire was to see the Duckweed in 

 flower before his death. 



