Distribution of the Laminar lacem. . 343 



on both sides at the base, but the characters of the stipe were ob- 

 scured in the specimen. 



In the subtribe Agareae then, we find four, or perhaps five genera 

 whose relationships both to one another and to the Laminarieae are 

 both complex and interesting. The lack of available material 

 further complicates this discussion as all the forms except Agarum 

 Tarneri are rarely found in herbaria. Agarum and Thalassio- 

 phyllum although so different in habit, are, as shown above, very 

 closely related and seem to be of a type thoroughly distinct from 

 the Laminaria-tj^e. But they are connected with it both by Cos- 

 taria and by Cymathmre. Costaria is the nearer to Agarum in 

 general habit. It has peculiar swellings and perforations of the 

 blade that are very similar to those in Agarum and in habit, color, 

 and internal structure the two are very similar. In both, the blade 

 is ribbed with the differences noted above. But Costaria lacks the 

 peculiar scrolls by which the blade of Agarum unrolls itself at 

 the base, and in this respect it resembles the Laminar ia-tj'pe. 

 Cymathcere on the other hand seems to be between Costaria and 

 Laminaria, resembling the former in possessing ribs (or "plicae"), 

 and yet probably destitute also of the scrolls at the transition- 

 place. Arthrothatnnus might perhaps be considered as intermediate 

 between Agarum and Thalassiophyllum on the one hand and 

 Laminaria on the other. The blade is neither perforated nor 

 ribbed, and yet it possesses the involute scrolls of Agarum at the 

 base and the spirally scarred stipe of Thalassiophyllum.. 



Lessoniideje. — Under this tribe are reckoned the five genera; 

 Lictyoneuron, Lessonia^ Postelsia, JSTereocystis, and Macrocystis. 

 All of these genera are much more complex than any of the Lamin- 

 ariidese. The fronds in all except Lictyoneuron are branched and 

 this branching originates in a splitting at the transition-place as 

 mentioned above. As to whether this splitting divides the blade at 

 whose base it occurs, equally or unequally, we have two subtribes 

 established, viz: the Lessoniese, comprising the first four genera and 

 the Macrocystese, including the genus Macrocystis. 



Subtribe 1 . Lessonese. The four genera Lictyoneuron, Lessonia, 

 Postelsia, and Nereocystis form a very natural subtribe of the Les- 

 soniidese. Their relationships are briefly discussed below. 



Lictyoneuron, Rupr. — There is only a single species belonging to 

 this genus. It inhabits the Californian coast and is rather rare. 



