290 BOTANICAL GAZETTE [ NOVEMBER 
Descriptive. 
A species of Stigeoclonium (perhaps a form of S.. tenue), 
found growing with Pleurococcus, etc., on moist bark at Ann 
Arbor, was chosen for experimentation. It shows two very distinct 
and easily distinguishable forms according to the culture medium 
in which it is grown. The normal form is that of Palmella. A 
culture of this form shows the surface of the fluid covered with : 
spherical cells 12 to 15m in diameter. The cells multiply by 
division in planes generally vertical and at right angles to each 
other, and the daughter cells separate more or less completely 
after division is accomplished (figs. 7, 6, 72, 27). The walls are 
quite thick and somewhat gelatinous on the exterior, though not 
by any means so markedly as in the form studied by Cienkow- 
sky (/.c., 2),and the protoplasm is quite coarsely granular. The 
chloroplast has the form of a hollow spherical shell with aa 
opening in one side, which has a diameter about equal ad the 
sphere’s radius, varying somewhat in different cells. Sometimes 
the opening is nearly a great circle of the sphere (fig: 4% i) 
This opening in the chloroplast is probably the “bright spat” 
described by Cienkowsky. There is always a pyrenoid present : 
in each cell, and sometimes two are found. This body has # : 
diameter of about 3m, and lies in a thickened region in ie | 
chloroplast. When the cell is about to divide the chloroplast 
separates into two parts, each part taking a half of the orig!” | 
pyrenoid, and a wall forms between the two portions (fig. 7 ¢)- : 
The plane of division always intersects the plane of the - e 
in the chloroplast. Then the two hemispherical cells: Decor 
more and more spherical, splitting the wall between 
its middle lamella, until finally, if nothing prevents, 
to lie as two separate spheres side by side (fig: shes “fg and 
often division proceeds more rapidly than this rounding - with : 
there results a group of four or more cells making cone : 
each other in plane surfaces (fig. 6). Often thi 
tinued without any parting till there results a 
spread out over the surface of the nutrient medium. 5 of the. 
too, the planes of division lie parallel to the surface 
