132 MOUNTAIN AND MOORLAND 



and only partly in the water is the perennial Reed 

 (Phragmites communls\ growing six to ten feet high, 

 a true grass; the Bulrush (Scirpus lacustris), some- 

 times eight feet high, a sedge; and various Rushes 

 (Juncus), which belong to a third family. We may 

 also find some of the following : The Water Plantain 

 (Alisma plantago\ the Flowering Rush (Butomus 

 umbellatus), and the Arrow-Head (Sagittaria sagitti- 

 folid), all belonging to the same family of Alismacese, 

 and most likely to be found on the sides of streamlets 

 entering the lake. Common along the water edge is 

 the Lesser Spear- Wort (Ranunculus lingua), a per- 

 ennial buttercup with elongated narrow leaves. 



A little farther out is the zone of Water-Lilies and 

 a belt, like a little forest, of Mare's-tail (Hippuris 

 vulgaris), with erect, many-jointed stem and whorled 

 leaves. Farther out still is the slender submerged 

 Naias flexilis, whose name means " water-nymph," and 

 there are also submerged species of Pondweed (Pota* 

 mogetori) along with others whose leaves and flowers 

 are on the surface. We found a little lake once the 

 floor of which was covered as far as we could see 

 with a growth of the Stonewort (Chara\ which gets 

 its name from the amount of lime that it deposits in 

 its cell walls. The two kinds, Chara and Nitella, form 

 a class by themselves, distantly related to Algae. They 

 are well known for the display of moving living 

 matter that is seen round the inside of the cells when 

 examined under the microscope, and Chara crinita is 

 famous because only female plants occur in Northern 

 Europe. The submerged Nitella meadows of Lake 

 Constance occasionally extend to a depth of over 

 fifteen fathoms, beyond which the light becomes too 



