THE ALGAE 151 



The thallus is filamentous, freely branched and gelatinous in texture 

 (Fig. 139). The central filament is made up of a single row of large cells, 



Carpo- 

 spores 



Fig. 139. — Batrachospermiim moniliforme. A branch of the Hving 



plant, enlarged. 



from which whorls of dichotomous lateral filaments are developed at frequent 

 intervals. Growth is by means of a single apical cell, which cuts ofi" cells 

 basipetally by transverse divisions. Immediately behind the growing point 

 these cells, which form the central filament, cut off small lateral cells, four 

 from each central cell, and these form the initials from which the side branches 

 arise. The lateral cells, though actively dividing, remain small themselves, 

 while the cells of the central filament elongate considerably, so that eventually 

 the groups of lateral cells are widely separated and appear to form nodes on 

 the axis. From these nodes grow out the richly branched clusters of side 

 shoots, which give the whole axis that beaded appearance to the naked eye 

 from which the specific name of " moniliforme " is derived. 



In addition to the side shoots the cells at each node give rise to filaments 

 which grow longitudinally dow^nwards to the next node, covering the axis 

 cells with a loose mantle or pseudo-cortex. Here and there also one of the 

 nodal cells is transformed into an apical cell and gives rise to a secondary 

 long shoot which repeats the structure of the main axis. The cells of 

 the lateral branches contain several irregular plastids, which are termed 

 chromatophores, each possessing a single pyrenoid. 



Sexual Reproduction 



The sex organs may be produced on the same or on diff'erent plants. 

 The male organ is the antheridium, but the female organ is called the 

 carpogonium and differs in some respects from the oogonium of the other 

 groups of z\lgae. 



