60 



PLANT STUniES 



greatly that the working 2)ower of the leaves is rediieed. 

 At no very great depth of water a limit is reached, beyond 

 which the light is no longer ahle to be of service to the 

 leaves in their work. Hence it is that water plants are 



restricted to the surface' of tlie 



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 a.nd ihxit 

 them, as seen in water lilies, (bus 

 obtaining light of undiminished 

 intensity. 



40. The climbing type. — Idindi- 

 ing stems are developed especially 

 in the tropics, where the vegeta- 

 tion is so dense and oversliadow- 

 ing that many stems have learncil 

 to climl) ui)on the bodies of other 

 plants, and so spread their leaves 

 in better liglit (see Figs. .">(>, .">."i, 

 OS. ]!»!»). (ireat woody vines 

 fairly interlace the vegetation of 

 tr<ipii'al forests, and ai'e known 

 as "lianas," or "lianes." The 

 same habit is noticeable, also, in 

 our teni])erate vi'getation. but it 

 is liy no means so extensivclv dis- 

 played as in tlic ti'opics. 'idicre 

 are a good manv forms of i-linili- 

 iiig stems. Remi'iidieriiig that 

 the liaJiit- refers to one slriii dc- 

 ](eH d i n g u jion a n <it li c v I'nr 

 mechanical sujiport, we ma\- in- 

 clude many liedgc ])lants in the 



Flu. 50. A \ iiif or liaiiii climbing 

 tile tniiilt of ;i trci', I'lu' leaves 

 are all adjusted to fuee the liglit 

 and to avoid eliading one an- 

 otlicr as far as pussiljle. 



