36. 
37- 
38. 
39. 
40. 
41. 
136 
Thallus at maturity hollow, with inner cortex of longitudinally 
running filaments, giving off closely set, radially arranged 
peripheral branches ; when young central part traversed by a 
single axial chain of cells ss ... Gloeosiphonia ...p. 
Thallus never hollow ; medulla of oe ee filaments or large 
cells, but without a distinct axial row.. -~ “f 
Thallus at first with a single axial row giving off whorls of cuit 
forked lateral branches; central axis reinforced later by 
downwardly-growing filaments (distinguishable from Nemalion 
by presence of whorled lateral branches) Dudresnaya ...p. 
Thallus simple or more or less dichotomously branched ; cortex 
of radiating filaments, separable under pressure and not 
forming a pseudo-epidermis ; cystocarps terminal on short 
branches not surrounded by special investing filaments 
Nemalion ...p. 
Thallus dichotomously branched, cylindrical, with a surface 
layer of colourless cells united into a pseudo-epidermis ; 
embedded cystocarps opening by a pore to the exterior 
SOUNAIA 5D. 
Thallus with distinct main axis and lateral branches ; cystocarps 
surrounded by special investing filaments 
Medulla formed of a bundle of attenuated filaments giving off a 
cortical system of radial branches Helminthocladia ...p. 
Medulla formed of large cells elongated in the direction of the 
axis, interwoven by narrow filaments, and covered by groups 
of radiating branches which, in youth, end in colourless hairs... 
Helminthova ...p. 
Plant cylindrical, sometimes slightly flattened; with a smooth 
outline or articulated into separate segments but not ee 
distally into narrow blades 
Plant with a stem- ate passing gradually into a distally 
expanded blade : ; é 
Thallus_ consisting ae ee of an exponen eae 
sometimes with veins but without a definite midrib; with or 
without a short inconspicuous stem aise ee Sac 
Thallus with stem and leaf-like appendages; or with distinct 
midrib and lateral laminae; vegetative aR marked me 
definite apical cell a a : re 
Thallus expanded into a much Granenedl fern- Bhs frond ae 
narrow segments not more than 4 inch in breadth . 
Branches opposite; thallus tri- or quadri-pinnate with very 
narrow linear segments ; a hig axial row of cells discernible 
in the ultimate branches.. ie as one 
Branches alternate lapposiek or whorled in Lauvencia obtusa) 
Thallus rigid, usually stiff enough to retain its shape when held 
out of the water; regularly quadripinnate, with alternate 
IOo 
: om 
I0O 
38 
78 
50 
58 
45 
44 
40 
41 
42 
long and short branches corticated to their tips... Ptilota ...p.97 
