1025] Setchell-Gardner : Melanophyceae 623 



other tissues of the blade, whereas in Costaria the tissues are uniform 

 among the bullae, between the five longitudinal costae. The so-called 

 "midrib" represents only a very slight modification of the blade. The 

 histological characters are the same as the remainder of the blade. 

 The part between two parallel longitudinal nerves is usually smooth 

 and free from cross nerves and is only slightly thickened at the 

 margins. The stipe in Dictyoneuriim is erect only in the juvenile 

 stage, soon becoming prostrate and attached by secondary hapteres, 

 only the short terminal portion remaining erect. That of Costaria 

 always remains erect. Dictyoneurum is perennial, lasting as long as 

 it can maintain attachment, and new blades are constantly being 

 formed. Costaria never fruits more than once. 



50. Nereocystis Post, and Rupr. 



Holdfast of a dense, interwoven mass of strong branched hapteres ; 

 stipe much elongated, slender, solid and cylindrical from the base 

 through the most of its length, enlarging above into a thick hollow 

 tube, contracting suddenly at the outer end just below the large, 

 terminal, spherical pneumatocyst, which bears at its summit a row of 

 short dichotoraous branches, on the ends of which are the long, narrow, 

 thin blades which bear the sori. 



Postels and Ruprecht, Illus. Alg., 1840, p. 9, pi. 39, figs. 24-30. 



Nereocystis differs so greatly in aspect from any species of Lessania 

 and even more so from the single species of Dictyoneurwm that the 

 resemblances are more in need of emphasis, in order to justify associa- 

 tion in the same tribe of the same family. In Nereocystis the first 

 segment of stipe is so long, so swollen, and the pneumatocyst so large, 

 while the branches (above the pneumatocyst) are so abbreviated and 

 condensed, that the Lessonia relationship is obscured, but becomes 

 plain on careful analysis. While Nereocystis differs so greatly in 

 aspect from other members of the Lessonieae, it resembles in the modi- 

 fication of the stipe, at least, Pelagophycus, of the tribe Macrocysteae, 

 so nearly that one must realize the significance of the unilateral branch- 

 ing of the stipe in the latter to feel justified in separating the two. 

 Postelsia>, however, is closely related to Nereocystis, the difference 

 between the main types of the type species of the two genera, apart 

 from dimensions, consisting largely in the development of a globular 

 pneumatocyst in Nereocystis, and the lack of such a terminal globular 

 inflation on the main stipe of Postelsia. The blades are much more 

 differentiated in the latter genus. 



