ORDER LEMNACE.E, OR DUCKWEED TRIBE. 513 



means cut-mouth) from the injury done by the sharp leaves 

 to the mouths of the cattle that browse upon them. There 

 is a marked difference in the properties of the two groups ; for 

 the British species of Butomus is one of the most acrid of our 



plants, its leaves being sometimes 

 used as a purgative; whilst the 

 Alismaceae are much less so, their 

 rhizoma or horizontal stem, which 

 is fleshy in some species, being 

 eaten as food by the Tartars and 

 Chinese. 



690. The next two orders, both 

 consisting of aquatic plants, may 

 be considered as presenting a near 

 approach to the aquatic Crypto- 

 gamia in general structure ; and 

 some species are very like Algje 

 in external aspect. They are 



FIG. 184BuroMUS. f J , 



clearly separated from them, how- 

 ever, by their organs of fructification ; but these seem reduced 

 to almost their simplest possible form. In the common Duck- 

 weed, for example, of which almost every pond will supply 

 us with specimens, the whole plant consists of a little green 

 scale, looking like a leaf, but really a compound of stem and 

 leaf, from the under side of which, as it floats on the water, 

 hangs down a single root-fibre. Few persons are aware that 

 the Duckweed ever flowers ; indeed there are some kinds which 

 appear to reproduce themselves only by buds, as no organs of 

 fructification can be detected ; but, if properly sought for, the 

 flowers of this little plant may usually be seen in the months of 

 June or July. If the eyes be attentively fixed on a mass of it, 

 on a still sunshiny day, a few minute straw-coloured specks may 

 very probably be discovered here and there upon the edges of 

 the plants ; they have a sparkling appearance, which attracts 

 observation. These are the anthers ; and if the plants possess- 

 ing them be more carefully examined, especially under a micro- 



