FEB. 1911.T NAKANO.—THE VEGETAT. OF LAKES AND SWAMPS. 47 



depth of water. In the eastern part of the swamp, an 

 immensly wide area is shallow and affords a very profitable 

 residense to the littoral flora. Also in the inlets of the swamp, 

 which are usually very calm and shallow, there occurs the vigo- 

 rous vegetation of marsh plants. Indeed, in the shallow parts 

 of the swamp, there always occur Zizania-Sind Phragmites-zone 

 even in the midst of the swamp; for example, along the '^Sengen" 

 embankment which proceeds to the midst of the swamp. 



b. Hydrodynamic factor. 



Submerged hydrophytes can live in open water, while swim- 

 ming hydrophytes always find their favorable residence among 

 Zizania-, Typha-, and Phragmites- zone, which all give them a 

 shelter against strong winds and waves. 



It is said that the extinction of three species, Brasenia 

 peltata, Euryale ferox and Trapa hispinosa in the Typha- zone 

 of the middle and western portions of the swamp occurred 

 during the flood in 1882 when the flow of the Tone flooded 

 over the swamp from its eastern valley. This may be true, 

 because it can be accepted that these three plants in the eastern 

 part of the swamp, on account of its wide area, survived a 

 little, while these of the coi-responding zones in other places were 

 wholly destroyed. We ma3' here imagine that the violent 

 obstructions of their respiration and assimilation, caused by 

 high w^ater and muddy particles, was a main cause of their 

 extinction. Here, we shall not also forget to consider the 

 mechanical disturbance of the flood. 



C. Edaphic factor. 



Reed^^ found in one of " Sister lakes " that humus soil is 

 very favorable for Typha, Nymphasa and Carex, and calcareous 

 soil for Chara, Potamogeton, Scirpus lacustris &c. Warming ^^ 

 also suggests that the former is particularh' associated with 

 nymphaceous vegetation. My observation agrees w4th theirs, 

 because Nymphaea tetragona, var. angustata is accompanied 



1) I.e. p. 135. 



2) 1. c. p. 65. 



