50 PLANT LIFE 
degree of cellular differentiation is really not 
essential for water plants, and we shall find 
that the complex structure of terrestrial 
species becomes simplified in any descendants 
that may have taken to a watery habitat. 
Even amongst the alge high differentiation 
of external form is not necessarily associated 
\ 
N 
Fo ty 
Fig. 7.—Caulerpa Stahlii. 
with a cellular complexity of corresponding 
magnitude. This is well seen in those sea- 
weeds that consist of a large number of cells 
which, though enclosed in a common peri- 
pheral membrane of cellulose, are not parti- 
tioned off from each other by cell walls. An 
example of such a plant, which combines 
a somewhat highly differentiated external 
form with an internal structure of remarkable 
