1917 Muenscher; Key to Phaeophyceae 253 



WW. Plants small, 5 cm. to 2 meters when mature. 



Y. Branches dichotomous, usually flattened, with swollen tips. 

 Z. Branches with midrib ; oogonia with 8 eggs. 



27. Fucus (p. 274) 

 ZZ. Branches without midrib ; oogonia with 2 eggs. 



a. Eggs of equal size. 28. Pelvetia (p. 276) 



aa. Eggs of unequal size. 29. Pelvetiopsis (p. 276) 



YY. Branches not dichotomous, only the lower branches flattened; 

 upper branches terete, with many small air bladders. 



30. C.ystophyllum (p. 276) 

 VV. Plants without air bladders or swollen tips, 

 b. Branches large, flat, blade-like, 

 c. Stipe prominent. 



d. Plant with several to many nearly equal blades on the end 

 of the stipe. 



e. Stipe thin, solid terete or flattened. 



11. Laminaria, split forms (p. 262) 

 ee. Stipe thick, hollow, terete. 31. Postelsia (p. 277) 



dd. Plant with a terminal blade and several lateral blades near 

 the end of the solid stipe. 



f. Terminal blade with a midrib; stipe plastic, thin, about 



1 cm. in diameter. 32. Alaria (p. 277) 



ff. Terminal blade without a midrib; stipe erect, "woody," 

 thick, about 2 to 5 cm. in diameter. 



33. Pterygophora (p. 280) 

 cc. Stipe very indistinct, short. 



g. Stipe widening into a ribbed blade from which large blades 

 arise oppositely ; blades with delicate ribs and serrate 

 edges, sometimes branching again. 



7. Desmarestia ligidata (p. 258) 

 gg. Stipe short; branches dichotomous, flat, spreading fan-like. 



34. Dilophus (p. 281) 



bb. Branches small, terete, coming from a more or less solid axis. 



h. Plant with one distinct central axis with many lateral branches 



that seldom branch again. 



i. Plant composed of closely compacted cells, center solid or 



hollow, peripheral layer tough ; growth apical. 



35. Chordaria (p. 282) 



ii. Plant soft, composed of loosely interwoven filaments, growth 



intercalary. 36. Castagnea (p. 282) 



hh. Plant without a distinct central axis; branches of different 



lengths, repeatedly branched. 37. Mesogloia (p. 282) 



