HOW TO KNOW THE SEAWEEDS 



183a Thallus with a large, central axial filament running through the 

 medulla 184 



183b Thallus without a large, central axial filament, but with very 

 slender, wire-like rhizoidal filaments packed in longitudinally be- 

 tween the large medullary cells (See Fig. 73) 185 



184a The large central axial filament with one or more similar but 

 smaller fUaments on either side. Fig. 229 Pikea 



Fig. 229. Pikea caliioinica 

 Harvey 



Transection of a mature 

 part of a plant to show the 

 aspect of the central axial 

 filament and of the two simi- 

 lar filaments on either side, 

 X 55. This species occurs 

 along the entire Pacific 

 Coast and in southern Cali- 

 fornia is often accompanied 

 by P. pinnata Setchell. It is 

 often 10 to 20 cm. tall, and 

 its branching may be- described as repeatedly and rather densely and 

 irregularly alternate-pinnate. P. pinnata is more regularly pinnate with 

 all the branches in one plane. 



Figure 229 



173 



