608 MINNESOTA BOTANICAL STUDIES. 



tion of green cell contents becomes gradually greater in each 

 successive cell as the apex is approached, the end cells being 

 generally quite filled (PI. XXXII, fig. 2). The chlorophores 

 consist of flat, circular plates (PI. XXXII, figs. 7, 8). The 

 pyrenoids are prominent and lie embedded in the proto- 

 plasmic matter. They often measure from 2 to 3 mic. in 

 diameter. 



It is a fact that no fresh material has shown bristles. The 

 apices of the branches are subulate with no evidence at all of 

 hyaline chaetophorous prolongations (PI. XXXII, figs. 1, 2, 3). 

 After the first few days, however, these make their appearance 

 in the greatest abundance. On the tenth day after the first lot 

 of material was taken from the spring, the bristles were first 

 observed. They grew from cells near the basal cells, that is, 

 from upright filaments containing only two to four cells (PI. 

 XXXII, fig. 4). They were also developed directly from the basal 

 cells (PI. XXXII, fig. 5). Ordinary vegetative filaments grew 

 from the adjoining basal cells. The bristle shown in fig. 5 is 

 160 mic. in length. 



The branches in general and sometimes the branchlets of the 

 filaments are terminated by very long and robust hair-like 

 growths which are multicellular in structure. It is usual for 

 the first colorless cell at the end of a filament to taper abruptly 

 from the width of the ordinary vegetative cell to about one-half 

 as much (PI. XXXII. fig. 6). The remainder of the cells become 

 more gradually attenuated until the apex is reached where a 

 somewhat bulbous knob is formed. 



A bristle 175 mic. in length had a terminating cell 25 mic. 

 long with a diameter of 2 mic. The longest cell which is near 

 the middle was 45 mic. in length. The diameter of the lowest 

 cell was 4 mic. In another case the length was 350 mic. and in- 

 cludes five cells, three of which are very long, while the two 

 next the vegetative cells are very much shorter. The end cell 

 was 110 mic. in length, the next two averaged 85 mic. apiece, 

 while the short ones were each 35 mic. in length. A bristle 

 measuring 500 mic. from base to tip terminated a branch of 

 vegetative cells. Another displayed a length of 650 mic. Near 

 the base it had a diameter of 7.5 mic, while at the tip it was 5 

 mic. across. It is more common for them to be extremely fine 

 at their extremities. The longest example noted was 1000 mic- 

 from the last vegetative cell to the tip of the filament. 



Prom the first the contents of some of the apical cells were 

 found to be in process of division. They were divided into 



