74 
SPOROCHNACEiE. 
IV. 
tufts along tliem ; 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 plants of deep water, none grow- 
ing in places where they are left dry at the recess of the tide, and veiy 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. Bossii ) 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 peduncidatus , 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 different aspect of the fruit in this Order forces us to group the 
genera under two families, yet there is such a peculiar habit common to all 
the individuals of the group, that authors scarcely differ in the limits they assign 
to it. Agardh and Kutzing 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 Dictyotaceax 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 Sporachnaceie 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 following genera belong to the sub-order Arthrocladieas. 
