1900] CHANGE OF FORM IN GREEN ALGH 291 
medium as well as perpendicular to it, and a parenchyma-like 
mass of polygonal cells is formed, projecting down into the fluid 
and up into the air (figs. 6, 2g). After division the chloroplast 
enlarges until it occupies about as much of the daughter cell 
asthe mother chloroplast did of the mother cell. The form 
just described will be termed throughout this paper the palmella 
form 
In the other form we have a very different mode of growth. 
The cells are not spherical, but cylindrical; they divide, except- 
ing at the origin of a branch, only by transverse planes, and 
show no tendency to break apart, but remain closely connected 
to form branching filaments (jigs. 2,8,18). This will be termed 
in the following discussion the filamentous form. The cells of 
the filaments are 4.5 to 10m in diameter and from two to four 
times as long. The longest filaments are 175 to 200p long and 
their branches extend in all directions. No true hairs have been 
Seen, but often the tips of the filaments are very narrow. The 
protoplasm is not granular, as in the palmella form, but usu- 
‘lly contains two to seven refractive bodies smaller than the 
Pyrenoid, but looking much like it. They are probably of an 
eS tatare. They have a diameter of about 154, that of the 
Pyrenoid being, as in the other form, about 34. The chloroplast 
elongated to suit the cell and becomes somewhat trough- 
shaped ; lying along one side of the cylindrical wall it reaches 
eee vee half way around the cell and usually partially covers 
nd, sometimes both. Its opening is thus longer than in the 
eer. The pyrenoid lies somewhere in a thickened part 
- Of the chloroplast. 
Reproduction in both forms is accomplished by comparatively 
of ts “xual biciliate zoospores. These are the nice 
chlor, “bs. I have observed no conjugating ZOOspores. ; 
Splast of the mother cell divides into four to eight parts 
ee “unously parallel planes running nearly at right 
its ag of the opening (fig. 7). Each of these portions, _ : 
oe ot the protoplasm, becomes a zoospore. Afier division 
is, ae 
© °mplete and the zoospores are nearly formed, the ne 
