

PLANT GEOGRAPHY 465 













c= SS 

= Fi SSS Se 
) PVR E ETT TS 
FIOSTHUNT TT 



































Fic. 518. Jussiaea repens, a rooting 


or floating aquatic with numerous in- 
flated roots which project upward into 
the air 

















These roots contain a great develop- 
ment of air spaces through which air 
can pass to the submerged portions of 
1 
the plant. (x 4) 




















































raises the level of the soil, while 
at the same time the stream, 
= leaving the lake, wears down its 
= bed and thus lowers the level 
a of the water in the lake. As 
the water becomes shallower the 
submerged plants will invade 
the bare area toward the center 
of the lake, while the plants 
with floating leaves will invade 
the areas formerly occupied by 
submerged plants. Likewise, the 
erect monocotyledonous plants 
will invade the areas previously 
occupied by the plants with floating leaves, while the forests will 
invade the area which was swampy as the latter becomes dry. 


































































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