

INTRODUCTION LOPLANT BISTOLOGY 45 
forming a tissue always have a common origin; they are 
interdependent ; they act together in order to perform some 
definite work for the life of the plant as a whole, and their 
mode of growth is similar. There may be a considerable 
amount of differentiation, even in such lowly organised plants 
asthe Alow. Thisis well illustrated in the seaweed Laminaria. 
Fig. 10 gives part of a section of the shoot, which is easily seen. 
to be much more differentiated than that of Fucus. 

Fig. 10.—LAMINARIA. 
All these instances, taken from one of the lowest groups of 
plants, the Algw, show how tissues arise by differentiation. 
It is just this capability of division of labour which marks off 
a higher from a lower plant; we shall therefore expect to find 
many more tissues in Flowering Plants than in these Alge. 
Tissues of Lhe cells of which a Flowering Plant consists 
Flowering are either— 
Plants ; =e 
1. Meristematic (Gk. merizo, to divide) cells, 
similar to those found in Protococcus and Spirogyra, capable 
of division and, therefore, of forming new cells; or 
2. Permanent cells, which have lost the power of growth 
and which have become var In groups—1.¢., tissues—each 
with its definite work, 
The staminal hairs of Spiderwort (Tradescantia) are an 
42 
