HOW TO KNOW 'THE SEAWEEDS 



178a Branching opposite, but the two branches of each opposite pair 



not alike. Fig. 225 Plumana 



(also known in the literature under the name Ptilota) 



Figure 225 



Fig. 225. Plumana filicina (Fallow) Doty 



A single primary lateral . branch showing the opposite pairs of 

 ultimate branchlets and their dissimilarity, X 5. This is one of the 

 commoner of seven species of this genus which may be encountered 

 along the Pacific Coast. Although more characteristic of the northern 

 parts of the coast, three of them extend southward through southern 

 Cahfornia. Two other species inhabit Atlantic shores from New Jersey 

 northward, namely P. pectinata (Gunner) Ruprecht and P. sericea (Har- 

 vey) Ruprecht. 



The dissimilarity of ultimate branchlets should be observed in 

 young parts where the contrasts are usually more pronounced. 



Specific characters are to be found in the nature of the margins 

 of the ultimate branchlets and in the curvature and length of these 

 branchlets. Thus, in P. filicina the branchlets are serrate on both mar- 

 gins, while in P. densa they are serrate only on one. Both P. californica 

 and P. hypnoides have smooth margined ultimate branchlets, but in the 

 former they curve upward toward the branch apex while in the latter 

 they do not. All of these four species are common in CaHfornia. 



178b Branching alternate or irregular, or if opposite, the branches of 

 opposite pairs essentially alike 179 



169 



