

44 FLOWERING PLANTS 
threads separated from each other with needles, filaments 
like the one drawn in Fig. 8 will be almost certainly found 
amongst the material. This is Spirogyra ; it consists of cells, 
all exactly alike, each having the same essential structure 
described in Protococcus. Cell-walls are present between the 
cells, so that Spirogyra is multicellular. The portion of the 
protoplasm containing chlorophyll takes the form of spiral 
bands, hence the name. In this organism many cells are 
associated together ; each cell is capable of all the activities 
necessary to the life of a plant, such as breathing and the 
taking in of food material; there is no setting apart of 
a particular cell for any special work. The cells have the 
power of dividing, each growing half into a cell like the 
original. | 
If now the 
_ribbon-like 
brown seaweed Fucus be 
examined, it will be found 
that it has a far more 
complicated structure 
than Spirogyra. 
Fig. 9 is part of a sec- 
tion through the shoot. 
The cells forming the outer 
layers are very different 
from those of the mner 
layers. Here, then, it 
is clear that there is a 
setting apart of certain 
cells for special work— 
in fact, there is division 
of labour ; the outer cells 
_. protect the inner, which 
e, external protective layers; 7, In- eS 
ternal, looser tissue. are mainly concerned 
with the vital activities 
of the plant. A group of cells thus set apart for a particular 
work in the life of the plant is called a tissue. The cells 
Fucus. 

Pie. 9. Fucus. 


