ALG 105 
65. Ulothrix.—These are bright green, thread-like 
plants found in the shallow, moving water of streams or 
Jake margins, where they are anchored to sticks or stones. 
Each plant is a simple (unbranched) filament, composed of 
a single row of cells; and the cells are all alike excepting 
that the lowest one is usually colorless, and is elongated 
and more or less modified to act as a holdfast, anchoring 
the filament to its support (Fig. 97, A). With the possi- 
Tic. 97.—Ulothriz: A, base of filament, showing holdfast cell and five vegetative 
cells, each with a single conspicuous cylindrical chloroplast (seen in section) 
surrounding a nucleus; B, four cells containing swimming spores; C, one cell 
containing four swimming spores (a), a free swimming spore (b), a cell (c) from 
which most of the gametes have escaped, pairing gametes (d), and the resulting 
odspores (e); D, young filament from a swimming spore; E, oéspore growing 
after rest; F, o6spore producing swimming spores.—E and F, after DopEet-Porr. 
ble exception of the holdfast cell, in each cell there may be 
seen a nucleus and a single chloroplast of peculiar form, 
being a thick cylinder investing the rest of the cell-contents. 
As seen under the microscope in optical section, the cylin- 
