48 THE BOTAMCAL MAGAZISE. cyoi. xxv. No. sso. 



always b}^ a dense association of Zizania (t. i. in Trpha-zonc) 

 and Phragmites, where a deep layer of humus soil is deposited. 

 On the contrarj-, when Phragmites and Zizania associations 

 grow on the sandy basin, the\' have no Aj'/npiz^a -association 

 among them. 



Brand^^ states in his ecological study of *' Wiirmsee" that 

 Scirpus lacustris can grow on a hard ground, so that it comes 

 lakeward, while Phragmites communis comes landward, because 

 it needs a shrammy habitat. This explanation does not seem 

 to hold good in the swamp, for here the situation of Scirpus 

 lacustris L. var. Tabernasmontani Gmel { = Sc. Tabernsemontani 

 Praxt.) is so mudd^^ as in the Phragmites-zone, and indeed 

 Phragmites often can make a large association even on a sandy 

 basin. I think, therefore, that the difference of their habitats 

 was caused b}- that of their adaptation to water. 



That large associations of Brasenia peltata, Euryale ferox, 

 and Trapa bispinosa are found only in the eastern part of the 

 swamp, seems to be remarkably correlated with the deposit of 

 humus soil, which occurs most richh^ in that part of the swamp. 

 It is said that thcA' had been poor in the western portions of 

 the swamp even in old times, where they were destroyed by 

 the flood of 1882. Accordingly, and especiallj^ by the abund- 

 ance of other helophytes, the vegetation of the eastern part of 

 the swamp is generally rich and luxuriant. 



d. Human interference. 



This factor may be considered as another cause of the 

 extinction of Brasenia peltata, Euryale ferox and Trapa bis- 

 pinosa in the middle and western portions of the swamp. 



In this swamp, landmen endeavour to reclaim the shore to 

 extend their rice-fields. Then they collect the humus soil as 

 manure for their iiields from the bottom of the swamp. Thus 

 the tranquill bed of these plants is disturbed and narrowed, 

 and consequenth' the depth of the littoral part increases. Ac- 

 cordingly, the Typha-zone had been destro\'ed at many places. 

 In the above places, we can see only two littoral zones :— a loose 

 association of Zizania and a Phragmites-znnG. 



1) 1. c. p. 6. 



