186 BRITISH MARINE ALG. 
divided or once forked. This plant is extremely variable in the length 
and number of its fronds. Near high-water mark or in shallow pools, a 
single frond, or at most two or three, grow on the rocks, or are attached 
to limpet shells, about 3in. high, and of a pale brownish-red colour; 
while in shady rock pools, or as it approaches low-water mark, the 
fronds are densely tufted, are often over 16in. long, and of a dark reddish 
purple. There is a curious variety of this species called crispata, in 
which the fronds are flattened and very much curled or twisted. This 
form of the plant is found only in the neighbourhood of fresh-water 
streams, and is another of those peculiarities observable in some species 
of seaweeds, where their character, form, or colour, is merely altered by 
contact with fresh water, while with many others, and particularly so 
with nearly all the species of the Order Ceramiacew, destruction or dis- 
figurement is the immediate result. The stem and branches of Dumontia 
are at first tubular but solid, the internal portion being composed of loosely 
intertwining filaments ; but as the plant reaches maturity these filaments 
are absorbed, leaving the tubular stems and principal branches empty 
within. Favelle, or round clusters of spores are produced within these 
tubes and attached to their sides, being formed out of the cells of which 
the inner surface of the tubes are composed. 0b, Fig. 172, represents a 
portion of the tubular stem of Dwmontia, highly magnified, showing 
favelle attached to the inner wallof the tube. This peculiar production of 
the fruit in Dumontia serves to illustrate the characteristic title of this 
extensive Order, that of Cryptonemiacee, the spore-bearing organs being 
concealed or hidden within the substance of the frond. 
The curious plant, Spyridia filamentosa, was formerly included in the 
Order Ceramiacee, but it now forms the only British representative 
of the very small Order Spyridiacew; the name being from the Greek for 
a basket, in allusion to the form of the favellz of these plants. Fig. 173, 
a, represents a terminal portion of a branch of Spyridia filamentosa. 
I have met with this species in Torbay and in the neighbourhood of 
Plymouth, but on no other part of the British coasts. Most of the 
species of this small group of seaweeds are natives of warm climates, our 
own S. filamentosa being widely distributed; very abundant on ‘the 
American shores, frequent in the Channel Islands, and reaching, I believe, 
its northern limit on the southern shores of England. The fronds of this 
plant are from 3in. to 10in. high. They arise in bushy tufts from a 
discoid root, and are very irregularly branched, the main stems being of 
a densely cellular substance, and very obscurely jointed. The lateral 
branches are mostly short, but, like the main stems, are beset on all sides 
‘with short bristle or hair-like, mostly simple, but jointed scattered ramuli. 
The favellz, which consist of two or three masses of spores, are produced 
on a ramulus which is somewhat altered in form, being divided from 
the tip downwards, and thus constituting a trifid or quadrifid involucre, 
within which the roundish masses of spores are seated, as represented at 
b, Fig. 173, which is a highly-magnified portion of stem, branch, and 
