PLATE IV. 



Laminaria, page 29. 



Fi(/. 1, L. digilata; showing the form of the full- 

 grown frond. 2, the same, in the act of throwing off 

 the frond of the previous season ; both figures on a 

 reduced scale. 3, cross section of the frond. 4, 

 spores ; both magnified. 



