1906] SIMONS—SARGASSUM FILIPENDULA 179 
SUMMARY. 
Each stem, branch, and leaf structure develops through sic activi- 
ties of a three-sided apical cell. 
The thallus consists of three compact tissues, called for conven- 
ience the epidermal, cortical, and conducting tissues. The latter con- 
sists of only thin-walled cells in the leaves, but in mature stems con- 
tains both thick and thin-walled elements. A ring of thick-walled 
cells, which may have both a mechanical and conducting function, 
surrounds the thin-walled conducting cells in the center of the 
axis. 
The tissues normally contain much reserve material, a part of 
which is oil, and a part, whose nature is undetermined, appears to be 
a carbohydrate. 
Both the conceptacles and cryptostomata originate in a single flask- 
shaped initial cell which develops the entire structure. 
The first division of the initial cell results in two unlike segments: a 
large lower cell which develops the walls of the conceptacle and cryp- 
tostoma; and an upper cell, the tongue cell, which either remains 
inactive, divides to form a short filament, or degenerates. The “‘initial 
cell” of Bower is apparently the tongue cell, a product of the true 
initial cell. 
The conceptacle and cryptostoma are undoubtedly homologous 
structures. Every stage of development in both structures is the 
same, from the appearance of the similar initial cells to the develop- 
ment of paraphyses in the cryptostomata and sexual organs in the 
conceptacle. 
The paraphyses are developed sag i by the division of the 
lowermost cell in each structure. 
Spermatocysts or their degenerate representatives occur in some 
cryptostomata. Such conditions indicate that the cryptostomata have 
been derived from conceptacles whose sexual organs have become 
sterile. 
The spermatocysts develop as in other Fucaceae, each finally pro- 
ducing sixty-four sperms which are discharged from a partly terminal 
and partly lateral rent. 
The sister cell of an oocyst does not become a stalk and conse- 
quently the oocyst is an embedded structure. 
