939 



The Isoetes and the Characeae are altogether dislinct from the pha- 

 nerogams; they form spores abundantly and regularly. 



Beyond the Litorella association the lake-bottom, as ah'eady 

 stated, is soft and loose, and here the spot-bound piants and those 

 which wander superficially over the bottom are largely replaced by 

 others with rhizomes embedded in the mud and wilh stems on which 

 the inflorescences are carried up to the surface. Spot-bound species 

 are still represented, however, since the Isoetes and Nitella still survive 



Fig. 177. Kvanhauge" lake on Sydero, seen from a cleft above the valley. 

 has a flat sandy shore, while the outer is bound in by clifTs. The ! 

 (From photo. by E, Warming). 



The inner side of the lake 

 :a in the bacliground. 



in this' zone, while perhaps MyriophijUum alterniflorum and Potamoge- 

 ton piisillus must also be regarded as spot-bound. The last-named spe- 

 cies occurs rarely; it has no creeping rhizome, but propagates, on the 

 Færoes, entirel}^ by its winter-buds, which each year produce a new 

 shoot, hence it is analogous with an annual plant. This plant-associa- 

 tion I have named after the most characteristic and most frequent 

 species ihe Sparganiiim-Potamogeton association. It includes, 

 besides the species just mentioned: Sparganium affine, Potamogeton 

 gramineus, P. natans, P. perfoliatus, P. nitens and less frequently P. 

 alpinus and P. praelongus. Several of the Potamogeton-spec'ies have 

 submerged leaves only (P. perfoliatus, P. praelongus, P. nitens and 

 P. alpinus on the Færoes); others such as Sparganium, have floating- 

 leaves, which are ribbon-shaped, whereas in the pond-weeds (P. 



