THALLOPHYTA Dol 
In some species the zygospore is formed by the conjugation of 
two adjacent cells in the same filament (Fig. 347). In such cases 
projections grow from the adjacent ends of the two cells. When 
the projections meet, the walls are absorbed, so 
that the two cells are connected by a tube, through 
which the protoplasm from one cell enters the other. 

Fic. 348. Forms of Desmid 
Desmids are either single cells or cells joined together in filaments, They are 
related to Spirogyra. See Fig. 349. (x 220) 
Relationship. Spirogyra belongs to the order Conjugatae, which 
is characterized by the absence of ciliated gametes and zodspores. 
In all members of the order sexual reproduction is due, as in 
Spirogyra, to the conjugation of two similar or nearly similar 
cells. The order is a branch of the Chlorophyceae, and although 
the members do not possess ciliated cells, they were probably 
derived from plants which did have such cells. As the line of 
evolution shown by the Conjugatae appears to end with the order, 
it is regarded as a side branch of the evolutionary process in plants. 
CLASS PHAEOPHYCEAE (BROWN ALG) 
The Phaeophyceae are multicellular alge having a brown color, 
and for this reason they are called brown algze. The motile re- 
productive cells have two cilia, which are inserted on the side of 
a cell, instead of at the anterior end as in the Chlorophyceae. Like 
