96 LAMINARIACE^. — Thalassiophyllum. iv. 



naceous, soon drying ; that of the stipe and midrib more coriaceous, or cartilagi- 

 nous. The colour is a darkish olive-green, becoming brown in age. The leaves, 

 when full grown, are often ten or twelve feet in length, and two or three feet wide. 



Plate V. Fig^ 1. A young frond of Agarum Tumeric the natural size ; Jig. 2, 

 part of a thin vertical slice, through a sorus and the outer coats of the frond ; Jig. 

 3, spores, in their per ispores, from the sorus ; Jig. 4, a spore isolated: — all the latter 

 figures more or less highly magnified. 



2. Agaeum pertusum, Mert. ; "stipes compressed, coriaceous, continued^as a 

 scarcely widened midrib ; lamina membranaceous, its holes when young furnished 

 with a margin raised at one side, and formed by openings in the buUated mem- 

 brane." J. Ag. Sp. Alg. I. p. 142. Kutz. Sp. Alg. p. 580. Post, and Bupr. t. 23. 



Hab. Newfoundland, De la Pylceie (fide J. Ag.) 



I am not acquainted with this species, which is said to have the holes much more 

 irregular in shape and fewer in number than those of the preceding species ; also 

 of more equal size, and smaller, rarely two lines in width ; and that they arise from 

 the bursting of a bullated membrane. 



A third species (A. Gmelini, Post, and Rupr. p. U. t. 20, 21,j is described from 

 the Northern Pacific, characterised chiefly, as it would seem, by having a midrib 

 twice as wide as the stipes, and holes with undulated margins ; but I fear these 

 characters can hardly be considered as alone sufiicient to distinguish a species, for 

 I find among a number of specimens picked up on Nahant Beach, great diversity 

 in the comparative breadth of the midrib, and form of the holes. In some of my 

 specimens, where the leaf measures 26 inches in length, the midrib is but two lines 

 wide ; and in others of somewhat inferior superficies, it is at least five lines, the 

 stipe being in the same specimens but two lines wide. I find similar variations 

 in specimens collected at Halifax, and that it is impossible to fix limits between 

 those with narrow, and those with wide stipes. It will remain to be seen whether 

 observers on the shore can detect characters, existing at all ages, between those 

 specimens with wide midribs and those with narrow. In many that I possess, the 

 apex of the frond, both midrib and lamina, is strongly curved or hooked to one 

 side, and this seems generally to occur in those with wide ribs. 



VIII. THALASSIOPHYLLUM. Post and Rupr. 



Frond with subdistinct leaves ; the leafy expansions formed by the evolution of 

 lamina, spirally developed round a branching stipe ; each leafy-lobe ribless. 



