IV. 
ECTOCARPACEiE. 
133 
a multitude of minute cells, the central ones of which are frequently cubical, 
closely compacted together into a firm, somewhat horny, rigid substance. In a few 
cases the frond is unbranched (as in the genus Myriotrichia ) ; very generally it is 
much divided, either pinnated, alternately branched, or more rarely subdichoto- 
mous. In Cladostephus the ramuli are short, subsimple, whorled round the branches, 
and deciduous at the close of each season. In Sphacelaria and Chcetopteris the ra- 
mification is distichous, the lesser divisions being simply or doubly pinnated. In 
Ectocarpus the frond is occasionally subsimple, or but slightly branched ; but in by 
far the larger number it is much divided, either dichotomous or distichous, and alter- 
nately or oppositely branched, but the branches rarely approach so nearly together 
as to be pinnated ; this is however the case in E. Mertensii, In some few the thread- 
like fronds are bundled together into branching ropes, forming a sub-definite, 
sponge-like, compound frond. 
The fructification appears under two forms, sometimes both found in the same or 
on different individuals of the same species ; in other cases but one kind of fruit 
has been noticed on all the individuals of a species, and hence has been employed 
as a specific character. The spores are less commonly formed than propagula , by 
which name the secondary fruit is known, and are oval or spheroidal, dark 
coloured, dense, furnished with a hyaline perispore, and attached to the sides of the 
ramuli, scattered and without paranemata. The propagula , which are chiefly 
characteristic of Ectocarpus , where their modifications often afford the best specific 
characters, are lanceolate, linear or conical, sessile or pedicellate, or immersed in 
the substance of the branches, transversely striate and filled with dense endochrome. 
In Sphacelaria they are lodged in the distended tops of the branches. 
In substance, the plants of this Order are rarely gelatinous ; those of the first 
sub-order are rigid, in some almost horny ; of the latter sub-order soft, and soon 
decomposing after removal from the water. The colour varies from dark brown to 
pale greenish-olive, and is subject to little change in drying except on the applica- 
tion of artificial heat, when the olive tints are brightened into more or less vivid 
greens. 
This Order is closely connected with the last, from which it is known by the 
absence of a gelatinous matrix connecting the filaments into a compound frond, 
and by the spores being external, scattered, and unaccompanied by paranemata. 
The genus Elachista is in some respects intermediate, and has been referred by 
Prof. J. Agardh to the present Order ; but appears to me to be too intimately con- 
nected with Myrionema and Leathesia , both clearly belonging to Chordariaceae, to 
be separated from them. 
By Agardh, Endlicher, and formerly by Kiitzing, the two sub-orders defined 
below are separated as distinct Orders ; and by Endlicher they are placed widely 
apart one from the other. To me their connection appears to be close, and their 
difference chiefly technical, — one being a rather simpler expression of the other — 
and therefore I am unwilling to multiply needlessly the number of Orders ; par- 
ticularly when I find, in such plants as Ectocarpus Mertensii , an obvious passage 
from one sub-order into the other. 
