138 



THE ALGAE 



Cladostephaceae: Cladostephus {dado, shoot; stephus, crown). 

 Fig. 76 

 The plants, which are bushy in appearance, arise from well-de- 

 veloped holdfasts and are characterised by the ecorticate branches 

 being arranged in whorls with tufts of hairs just below their apices. 

 Cells just below the apex divide to give a number of branch seg- 

 ments, this type of branching being known sls polyblastic. The first 

 segment of these laterals of limited growth cuts off a cell or cells 



Fig. 76 Cladostephus verticillatus. A, plant ( x \). B, apex to show 

 origin of branch, ba = branch apex. C, thallus showing cortication. 

 D, unilocular sporangia ( x 225). E, part of thallus with unilocular 

 sporangia ( X45). (A, D, E after Newton; B, C, after Oltmanns.) 



that form a cushion of tissue belonging to the main axis. Later the 

 spaces between laterals may be filled by tissue so that the bases are 

 completely enveloped. As a result of this septation the older 

 branches, although originally hemiblastic in origin, appear to arise 

 only from the tops of the original superior segments. The lower 

 portions of the segments may later give rise to secondary whorls 

 which are said to arise merihlastically. The main axis is corticate 

 because both upper and lower primary segments undergo abundant 

 division. In addition the cells so formed enlarge in width and length 

 so that the axis increases in size from the apex downwards. Such a 



