60 
PLANT STUDIES 
greatly that the working power of the leaves is reduced. 
At no very great depth of water a limit is reached, beyond 
which the light is no longer able to be of service to the 
leaves in their work. Hence it is that water plants are 
restricted to the surface of the 
water, or to shoal places ; and in 
such places vegetation is very 
abundant. Water is so serious 
an impediment to light that very 
many plants bring their working 
leaves to the surface and float 
them, as seen in water lilies, thus 
obtaining light of undiminished 
intensity. 
46. The climbing type. Climb- 
ing stems are developed especially 
in the tropics, where the vegeta- 
tion is so dense and overshadow- 
ing that many stems have learned 
to climb upon the bodies of other 
plants, and so spread their leaves 
in better light (see Figs. 50, 55, 
98, 199). Great woody vines 
fairly interlace the vegetation of 
tropical forests, and are known 
as "lianas," or "lianes." The 
same habit is noticeable, also, in 
our temperate vegetation, but it 
is by no means so extensively dis- 
played as in the tropics. There 
are a good many forms of climb- 
ing stems. Remembering that 
the habit refers to one stem de- 
FIG. 50. A vine or liana climbing 
the trunk of a tree. The leaves pending Upon another for 
are ail adji^ted to face the light mec hanical support, we may in- 
and to avoid shading one an- r * . 
other as far as possible. elude many hedge plants m the 
