430 
THE SEAWEEDS 
Families ST1CTOSPORACEAE and SARCOD1ACEAE. 
The development of the gonimoblasts relates these famlies in some degree 
with the Plocamiaceae and Sphaerococcaceae. The formation of the pro- 
carp is not known. The gonimoblasts develop outwardly from the thallus, 
and their nutrition is derived only through the auxiliary cell. In Trema- 
tocarpus ( Sarcodiaceae ) a large abnormally branched fusion cell is formed. 
In both families the upper cells of the gonimoblast filaments usually form 
earpospores. The cvstocarp wall is particularly thick and has a distinct 
aperture. 
Family STICTOSPORACEAE. 
Stictosporum Harvey. 
Family GRACILARIACEAE Kylin 1930. 
Plants mostly branched, to even bushy, the branches slender to coarse, 
cylindrical to strap shaped, firm and often cartilaginous; axes developing 
from three-sided apical cells, ultimately forming a parenchymatous medulla 
and a narrow small-celled assimilative cortex which may bear delicate 
colourless hairs ; sporangia tetrapartite, scattered at the surface ; sperma- 
tangia scattered, cut off from surface cells; carpogenic branches of two 
cells, the carpogonium fusing after fertilization with the other unit of the 
carpogenic branch, the supporting cell and the sterile cell series which it 
bears, and then with several neighbouring vegetative cells which have 
become richly stored, the larg^e fusion cell thus formed giving rise to the 
gonimoblasts ; cvstocarp with a sterile central placenta and a thick project- 
ing pericarp opening by a pore. 
Melanthalia Montague. Curdiea Harvey. GracUaria Greville. T plot us 
J. Agardh. 
Families MYCHODEACEAE and ACROTYLACEAE. 
These families, with the above considered groups of the Gigartinales, are 
not closely related, but are obviously related in the development of the 
procarp to the Phyllopharaceae and Gigartinaceae, and appear to have a 
similar lowly evolution. However, in all forms of the Gigartinales the 
position of the auxiliary cell in the doubtful families is intercalated with 
a segmented cell in the thallus. This cell also serves as a supporting cell 
to the carpogonium. In the Mijchodeaceae and Acrotylaceae each support- 
ing cell forms more carpogonia which are situated laterally on the sup- 
porting cell. They are three celled in ILychodea and project straight out- 
ward, while in Acrotylus they curve in a characteristic manner. They are 
also three celled in Acrotylus, but the first cell forms a one-celled side 
branch. The second cell of the carpogonium is in Acrotylm considerably 
larger than the rest. 
