206 



This species has a well developed indusium and is further- 

 more characterized by the fact that the organs of propagation 

 and the series of hairs alternate regularly (Figs. 157, 158). 



At the extreme edge the thallus consists only of two layers 

 of cells, namely: a surface layer consisting of smaller cells nearly 

 square in transverse section and a layer of larger cells below. 

 These last mentioned cells are soon divided by horizontal walls 

 into a number of cells, varying somewhat in the different spec- 

 imens. The cell-layer below is again divided by vertical walls 

 into small cells similar to those of the surface. 



Fig. 159. Padina variegata (Lamx.) Hauck. 

 a, transverse section of the thallus with tetrasporangia. b, transverse sec- 

 tion of the thallus with oogonia. c, surface view of thallus with tetraspor- 

 angia. (About 90 : 1). 



The cells between the two epidermal layers are mostly rather 

 long and flat ; we find here up to six layers varying in the different 

 specimens. 



Lower down in the thallus near the base almost all the cells 

 are divided into smaller cells nearly quadratic when seen on 

 transverse section (Fig. 160 6). 



Hairs occur upon both sides of the thallus (Fig. 160 a) most 

 numerous upon the surface ; sometimes a corresponding series of 

 hairs are found upon both sides of the thallus. 



The rows of tetrasporangia are as already mentioned regu- 



