140 MOUNTAIN AND MOORLAND 



with Utricularia, which is, as we have seen, a rootless 

 plant with a long, trailing, submerged stem. Like 

 Utricularia, the Duckweeds form store buds in autumn 

 which sink into the mud and float up again in spring. 

 It is hardly necessary to say that unattached aquatic 

 plants, like Bladderwort and Duckweed, must be re- 

 stricted to stagnant water. 



It is difficult to believe that Lemna is a flowering 

 plant, but careful inspection will disclose on the edge 

 of some of the green discs the tiniest of flowers. 

 They occur in little groups, two male flowers with a 

 stamen apiece, and a female flower with one carpel, 

 the three being surrounded by a hood. There is another 

 kind of Duckweed, called Wolffia arhiza, which has 

 still smaller flowers and is rootless. It must be the 

 smallest flowering plant in Britain. 



We must not linger much longer over these water- 

 plants, interesting as they are, but it should be noticed 

 that besides the thoroughly aquatic forms like Bladder- 

 wort, Pondweed, and Duckweed, like the Water Star- 

 worts (Callitriche), where each male flower has one 

 stamen and each female flower one pistil, and the 

 Naiads with equally simple flowers, and the Horn- 

 worts, there are a number that live in the water with- 

 out being in any real sense water plants. Such is the 

 Bog Bean (Menyanthes trifolium), a member of the 

 Gentian family, with vigorous tripartite leaves and 

 handsome white flowers raised out of the water along 

 the edge of the tarn. 



On a high tarn in the North-west Highlands we 

 once saw an extraordinary display of the Water 

 Lobelia (Lobelia dortmanni), which occurs here and 

 there in North Europe, a good example of the way in 



