2 9 8 PETALOIDEA 



Natural Order XCIII 

 PISTIACE.E. Duck-weed Tribe 



Minute floating plants, composed of simple or lobed leaves, and 

 fibrous roots, which are not attached to the soil, propagating them- 

 selves principally by off-sets, but sometimes producing on the edge 

 of the leaves 1-2 stamens and 1- to 4-seeded ovaries, enclosed in 

 small sheaths. Lemna (Duck-weed) is the only British example, 

 and the number of foreign species is but small. 



1. Lemna (Duck-weed) 



1. L. minor (Lesser Duck-weed). A minute plant, but often so 



abundant as to cover the surface of stag- 

 nant water, where, with the insects which 

 it harbours, it is greedily devoured by 

 ducks. In this species the leaves are 

 egg-shaped, and bear each a single root. 

 Four other species have been found in 

 Britain, for a description of which the 

 Lemna Minor student is referred to Bentham and 



(Lesser Duck-weed) Hooker's " British Flora." 



Natural Order XCIV 

 NAIADACE.E. Pond- weed Tribe 



Submersed or floating aquatics, with very cellular stems and 

 peculiar leaves, which are sometimes almost leathery, but more 

 frequently thin and pellucid. The flowers are small, olive-green, 

 resembling in structure the Arrow-grasses ; sometimes solitary, 

 but more frequently arranged in spikes. They inhabit ponds and 

 slow streams, or rarely salt marshes. Our British species, Zostera 

 marina, grows in the sea. 



1. Potamogeton (Pond-weed). Flowers in a spike ; stamens 

 and pistils in the same flower ; perianth of 4 sepals ; stamens 4, 

 sessile. (Name from the Greek, potamos, a river, and geiton, a 

 neighbour.) 



2. Ruppia. Flowers about 2 on a stalk ; stamens and pistils 

 in the same flower ; perianth ; stamens 4 ; carpels 4, at first 

 sessile, afterwards raised each on a long stalk. (Named in honour 

 oi H. B. Ruppius, a botanist of the eighteenth century.) 



3. Zanntchellia (Horned Pond - weed). Flowers axillary; 

 stamens and pistils separate (monacious) ; stamen I ; carpels 4. 

 (Named in honour of /. /. Zannichclli, a Venetian botanist.) 



