THOMPSON: THE MORPHOLOGY OF TAENIOMA 99 
pusilum J. Ag. and not of 7. macrourum (Schousb.) Thuret. 
However, although it would seem probable that both of my speci- 
mens should be classed with 7. macrourum, a discussion of the 
classification would not be profitable here, since this work con- 
cerns itself not with a determination of species, but with a descrip- 
tion of the exact method of growth and cell division, and the 
appearance and formation of the reproductive organs. 
The species of Zaexzoma studied is a small marine alga, form- 
ing dense tufts on other algae, or on sticks of wood near the low- 
water line. It is purplish red or dark violet in color, and minute 
in size as to the individual plants, though forming, in mass, patches 
easily distinguishable. The main axis is monopodial, siphonous, 
branched, creeping, segmented, and not corticated, and is attached 
to the substratum by numerous rhizoids (Fic. 1). Branches arising 
from the main stem are in turn much branched, frequently forming 
long secondary axes, which are prostrate and produce rhizoids. 
The shorter secondary axes are erect, arising alternately from either 
side of the stem, those on the lower side twisting in the process of 
erection, so that superficially they appear secund. Both these and 
the main shoot bear short flattened shoots, arising alternately, and 
prolonged at the apex into two or three long monosiphonous hairs. 
Growth takes place by means of a single apical cell which is re- 
corded by Agardh (’63) as dividing dichotomously. Since the cell 
does not divide by a longitudinal split, as will be shown later, and 
since the main axis is monopodial, this cannot be considered true 
dichotomy, although the branching may be called subdichotomous. 
The rhizoids are numerous, arising irregularly, each being a 
direct prolongation of any pericentral cell on the under side of 
the thallus. They are unicellular, often of considerable length, 
with ends rounded or spread out into disks or forked projections 
(FIG, 2). 
The main stem or primary monopodial axis of the plant is 
composed of four pericentral siphons in protoplasmic connection 
with each other and with the central siphon. This latter forms a 
distinct core through the stem, the cells being elongated and 
closely joined, with deep pit connections. A stem segment is 
cylindrical, composed of four of these pericentral cells with the 
corresponding axial cell. No evidence of cortication has been 
