ALGJE 



105 



65. Ulothrix. These are bright green, thread-like 

 plants found in the shallow, moving water of streams or 

 lake 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- 



Fio. 97. Ulothrix: 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 (6), a cell (c) from 

 which most of the gametes have escaped, pairing gametes (d), and the resulting 

 oospores (e)j D, young filament from a swimming spore; E, oospore growing 

 after'rest; F, oospore producing swimming spores. E and F, after DoDEL-PoRT. 

 / 



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- 



