HOW TO KNOW THE SEAWEEDS 



11a Thallus usually of firm consistency, of more or less parenchymatous 

 type structure, at least in the cortical and outer medullary regions. 

 Fig. 22 18 



iTSt^ 



Fig. 22. Part of a transverse section 

 of Giacilaria to show the paren- 

 chymatous type, large, relatively 

 thin-walled, more or less isodia- 

 metrical cells of the medulla. In 

 this instance there is a gradual 

 transition from the largest medul- 

 lary cells to the small cells of the 

 cortex. 



Figure 22 



lib Thallus not of parenchymatous type structure, soft or firm 12 



12a Thallus wiry, rigid, cartilaginous, the medulla of densely packed 

 longitudinal filaments, the cortex of dense anticlinal cell rows. 

 Fig. 23 Ahnieltia 



Fi'g. 23. Ahnieltia plicata (Hudson) Fries 



A small portion of a plant to show the 

 cylindrical, regularly dichotomous branch- 

 es, X 1.5. This species occurs both in New 

 England and along the Pacific Coast. A. 

 concinna J. Agardh is a coarser species 

 of greater diameter which is found occa- 

 sionally along the Pacific Coast. 



Figure 23 



12b Thallus soft, spongy, or often gelatinous, (firm in Chordaria). con- 

 sisting of variously branched, interlaced or intertwined filaments 

 which may be more or less compacted in the medulla but are 

 externally free ^'^ 



33 



