162 Rhodora [ AUGUST 
THE NEW ENGLAND SPECIES OF DICTYOSIPHON. 
F. S. CorLiINs. 
Tue genus Dictyosiphon was founded by Greville in 1830, on 
the Conferva foeniculacea of Hudson, which, for a long time, was the 
only species. There are now about ten species recognized, all but 
one inhabiting the North Atlantic and Arctic oceans, extending also 
a short distance into the North Pacific. The one exception, which, 
when better known, may have to be transferred to another genus, oc- 
curs in South Pacific and Antarctic waters. à 
The genus is characterized by a terete, more or less abundantly 
branched frond, growing by an apical cell, by whose rapid division 
and the repeated division of the segments cut off, the frond is formed ; 
consisting of an inner layer of rather large, loose, colorless cells, 
elongated in the direction of the length of the frond, and an exter- 
nal layer of small, roundish or squarish colored cells. Unilocular 
sporangia, spherical or flask-shaped, are formed in the cortical layer, 
immersed or slightly projecting; plurilocular sporangia are unknown. 
'There are two subgenera, characterized thus: — 
EU-DICTYOSIPHON. 
Species of large size, slender, filiform, little or not at all gelatinous; branches 
and ramuli not attenuate at the base; cortical cells small; sporangia usually 
scattered, single. 
COILONEMA. 
Of smaller size; branches of first and second. orders long, sub-simple, hollow, 
inflated, tapering to both ends, especially to the base; cells of the cortical 
layer large, rounded ; sporangia in groups. 
Not one of the characters given above, however, is always to be 
depended on; indeed, in a good proportion of individual plants, some 
characters of one subgenus will be found combined with characters 
of the other. 
Specific limitations are vague ; very distinct types can be selected, 
but all possible intermediate forms are found, and the determination 
of individual specimens is often a matter of considerable difficulty, 
and sometimes impossible. The following key will only approximately 
indicate the New England forms: 
Frond with stout percurrent axis and simple branches of nearly uniform length, 
D. Macounii Farlow, 
Frond quite slender, simple or with very few branches, 
D. Ekmani Areschoug. 
