Contribution. I. 



57 



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passes gradually into D. amplissimum f. tyinca, wbich has 

 sqnarish. or vertically rectangular cells by a tliickness usu- 

 ally varying between 50 and 60 [x, sometimes a little thicker, 

 sometimes tliinner. In Hauck et Richt. Phyk. univ. Nr. 

 8 such an intermediate form is distributed by Collins 



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under the name of Torphyra miniafa. It has the outward 

 appearance of D, ampUsshuum f. typiica but it is, at the 

 niiddle part of the frond, only 36 [i thick, and the cells are, 

 in cross section, horizontally rectangular, reserabling fig. 18 

 by Stromfelt 1. c. Anotherspecimq^i from Nahant, Mass., 

 comraunicated to me by Collins, coincides almost fuUy 

 with the typical form of D. tenuissimum. The frond is at 

 the middle 25 \i thick. I therefore think D. tenuissimum 

 ought to be regarded as a form of D. amplissimum. 



The typical form of D. amplissimum is distinguishing 

 itself by its darker colour, greater thickness and especially 

 by its being densely folded, «often so deeply that the folds 



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extend to the middle line of the frond». However fromthis 

 deep folding it passes gradually into quite smooth, and then 

 it approaches much to D. miniatum (Lyngb.).* Such a form 



\ I have only seen a eingle speciraen of I), ininiatmn, wliich I fouiid 

 sorae years ago at Gjesvær in WesL-Finmarken, attachedto the rudder 

 of a smaller vessel then caa-ymg trade between Gjesvær and Ham 

 inerfest. I gupposc this vessel the preceding year has becn m the 

 neighbourhood oi Spitzbcrgen, and there the spore has fastencd itself 

 to the rudder, because the species has not beenfoundcarlier nor late 

 at the coast of Norway. I have not succecded in getting accuratc 

 informations as to the route of the vessel that year. 



The spccimen in question accords well with the description given 

 by Lyngbye in Ilydr. Dan. t. 29, and the figures by Kutzing in 

 Tab. Phyc. 19, t. 81, and Kj e lim an in N. Ish. Algfl. t. 18, fig. 9. 

 The margin is irregulatly laciuia^e and somewhat denticulate, and the 

 middle of the irond has a thickness of 72 ]x. The specimen was col- 

 lected in the begimiing of September, bearing sporocarps and antheri- 

 dia. Thus this plant is not always dioecious. Cp. Kj eUm, N^ Isbj 



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