74 SPOROCHNACEJi:. iv. 



tufts along them ; while, in others {Sporochnus and Carpomitra) the fertile filaments 

 are closely packed together and combined into knob-like receptacles, in whose sub- 

 stance the spores are hidden. On dissection these receptacles are seen to be made 

 up of branching filaments, of some of whose branches the spores are formed ; and 

 they are either borne on minute, lateral ramuli (or peduncles), or terminate the 

 larger branches of the frond. 



A small group of plants, of which five or six genera, comprising about 24 species, 

 are at present known to botanists. They are all j)lants of deep water, none grow- 

 ing in places where they are left dry at the recess of the tide, and very few being 

 found much above low-water mark, and then only in deep and shady tide-pools. 

 They increase in numbers and in luxuriance of development at three or four 

 fathoms depth, and extend to fifteen or twenty fathoms, often constituting at the 

 bottom of the sea submarine fields of considerable extent. This is the case on the 

 North American coast with respect to Desmarestia aculeata, which, in deep enclosed 

 bays, like that of Halifax, is often the only plant that comes up in the dredge 

 after five fathoms of depth, and in many places it seems to choke all other 

 vegetation. A similar prevalence of two other species of this genus {D. chordalis 

 and D. Rossii) in the deeper parts of the Laminarian zone, has been noticed by Dr. 

 Hooker in the Antarctic Ocean. 



Several of the plants of this Order are widely distributed. All the American 

 species of Desmarestia have a range almost as wide as that of the ocean ; being 

 found in the temperate and colder regions at both sides of the torrid zone, and 

 extending almost to the limit of marine vegetation towards either pole. Their 

 reputed absence in the tropical waters is perhaps owing to a failure of observation. 

 Arthrocladia villosa, recently discovered in North Carolina, had been until then 

 supposed to be confined to the shores of Europe, where it almost always accompa- 

 nies Sporochnus pedunculatus, a species not yet added to the American Flora. The 

 genus Chnoospora is entirely tropical, but is found both in the eastern and the 

 western hemisphere. 



Although the dififerent aspect of the fruit in this Order forces us to group the 

 genera under two families, yet there is such a j)eculiar habit common to all 

 the individuals of the group, that authors scarcely differ in the limits they assign 

 to it. Agardh and Kiitzing coincide with the original view of Greville, which is 

 that here adopted; but Endlicher and following him, Lindley, reject Arthrocladia 

 and refer it to the neighbourhood of Cutleria in Dictyotaceae. A comparison of 

 the respective structure and development of Arthrocladia and Desmarestia viridis 

 will I think show that these plants cannot well be far separated. There is some- 

 thing so distinctive in the colour of the Sporachnacese when fresh, and the very 

 remarkable change which they undergo on exposure to the air, that these peculiar- 

 ities alone seem to point, as Mr. Dawson Turner has long since noticed, to a natural 

 affinity among them. 



All the follomno- arenera belong to the sub-order ARTHEOCLADiEiE. 



