210 ip 3 t C i 5 i a 



of the bladder. In the pith-web many 

 of the anastomosing tubes are joined 

 by flaring ends. These are the so- 

 called trumpet-hyphse. Reserve food 

 material is often stored in the pith. 

 Different genera of kelps have their 

 anatomical peculiarities; thus, in some, 

 mucilage ducts are formed in the 

 cortex, while in others they are quite 

 absent. In some, secondary thickening 

 of the stipe occurs. This is true of 

 perennial forms, such as Lessonia and 

 Pterygophora. Many of the largest 

 kelps, however, are annuals, and in 

 these, e. g. in Nereocystis, secondary 

 thickening will not be found. In Lesso- 

 nia or Pterygophora cross sections of 

 the stipe show rings of growth, in gen- 

 eral appearance not unlike those of an 

 exogenous tree. As a matter of fact 

 they are produced in a manner pecul- 

 iar to the kelp, but in so far as they 



