HOW TO KNOW THE SEAWEEDS 



Pjgure 209 



166b Thalli larger, 15-40 cm. tall; macrosporangla (oogonia) with two 

 functional spores. Fig. 209B Pelvetia iastigiata 



Fig. 209. 



Macrosporangia of two closely re- 

 lated genera: A, Pelvetiopsis, and B, 

 Pelvetia. These are shown removed 

 from the inner wall of the conceptacle 

 in which each was produced. In the 

 case of Pelvetiopsis a single functional 

 spore is seen, the remaining nuclei 

 from the divisions of the macrospor- 

 angium being separated off in a non- 

 functional mass below. In Pelvetia 

 two functional spores are seen with 

 the extruded nuclei between. Various stages in the development of 

 these macrospores as well as the microspores (antherozoids) may be 

 observed by cutting transections of receptacles bearing maturing con- 

 ceptacles. 



See note regarding Pelvetia under Fig. 208. 

 167a Medulla composed mainly or entirely of large, parenchymatous 

 cells 171 



167b Medulla not composed of large parenchymatous cells, but of 

 densely or loosely packed ramified filaments, mostly longitudi- 

 nally arranged 1^^ 



168a Flat surface of branches provided with small, wart-like or spine- 

 like papillae. Fig. 210 Gigartina (in part) 



Fig. 210. Gigartina stellata Bat- 

 ters 



An entire, maturing plant, X 1. 

 This species from the Atlantic 

 Coast, occurring from Rhode Is- 

 land northward, is illustrated as 

 an example of a rather diversified 

 group of Gigartina species which 

 . will best key out here. These are 

 all flattened, more or less clearly 

 dichotomously branched forms 

 bearing papillose or spinose out- 

 growths from the flattened sur- 

 faces of the broader blade parts. 

 About half a dozen Pacific Coast 

 species fall within this assem- 

 blage, of which G. cristata (Set- 



Figure 210 



159 



