180 
PLANT STUDIES 
out of water submerged plants which seem to be upright, 
with all their parts properly spread out. "When removed they 
collapse, not being able to support themselves in any way. 
(5) Development of air cavities. The presence of air in 
the bodies of water plants is necessary for two reasons: (1), 
FIG. 161. Bladderwort, showing the numerous bladders which float the plant, the 
finely divided water leaves, and the erect flowering stems. The bladders are also 
effective "insect traps,' 1 Utriculana being one of the "carnivorous plants." 
After KERNEB. 
to aerate the plant ; (2), to increase its buoyancy. In most 
complex water plants there must be some arrangement for 
the distribution of air containing oxygen. This usually 
takes the form of air chambers and passageways in the 
body of the plant (see Figs. 87, 88, 89, 90). Of course 
such air chambers increase the buoyancy of the body. 
Sometimes, however, a special buoyancy is provided for 
by the development of regular floats, which are bladder- 
