THE DUCKWEEDS. 46 



underside very pale green and slightly convex, with a single root. Spathe two- 

 lipped, one much larger than the other. Stamens two, one maturing before the 

 other ; style long. Flowering in July. 



II. Ivy-leaved Duckweed (L. trisulca). Frond thin and flat, nearly an inch 

 long, tailed at one end, coarsely toothed at the other. New fronds emerge at right 

 angles to the parent. Roots solitary. Stamens two ; style short. June and July. 



III. Thick-leaved Duckweed (L. gibba). Frond nearly round, narrowed at one 

 end, large, almost flat, green opaque on top, greatly swollen beneath, whitish, clear, 

 the cell-structure being very noticeable. Root solitary, stamens two. Flowers 

 June to September. 



IV. Great Duckweed (L. polyrhiza). At once distinguished from the others by 

 its bunch of roots from each frond. Upper surface slightly convex, dark green with 

 seven nerves. Underside purple, as also the upper margins. Stamens two. Flower 

 has been rarely, if ever, seen in this country. 



Late in Autumn the fronds sink to the bottom of the ponds and ditches, and 

 remain there hibernating till Spring, when they arise to the surface, and again 

 vegetate. The name of the genus is the old Greek appellation of the plant Lemna, 

 supposed to be derived from Lepis, a scale. 



Corn Chamomile (Anthemis arvensis). 



We have already described several species of Composite, and 

 now return to that order to describe a type of flower very 

 similar in general appearance to the Daisy (page i). The Corn 

 Chamomile is an annual plant ; the lower portion of its stem is 

 prostrate, sending up erect branches with alternate, prettily cut 

 leaves, twice pinnate. The flower-heads are borne singly on 

 long stalks, and the floral envelope (involucre] consists of a 

 number of over-lapping scales (bracts'), whose margins are dry 

 and chaffy. The base (receptacle} upon which the florets are 

 packed is convex and covered with little chaffy scales, which 

 stand up between the florets. The disc-florets contain both 

 anthers and pistil ; the ray-florets are pistillate only. The 

 whole plant is downy. It occurs in fields and waste places, 

 flowering from May to August. Though somewhat widely 

 distributed, it is a local plant. The name is an old Greek 

 name for the Chamomile, from anthemon, a flower, probably 

 owing to the profusion of its blossoms. 



The other British species of the genus are two only : 



