420 BOTANICAL GAZETTE [DECEMBER 
of the cystocarp becomes swollen and urn-shaped. This envelop 
is developed from the peripheral siphons of the procarpic branch; 
but is lined with a set of delicate filaments (jig. 132, p f), called 
paranematal filaments, that arise from the cell of the axial siphon. 
Some of the gametophytic nuclei derived from the auxiliary cells 
break down before the unions or after the formation of the central 
cell. They swell greatly, the chromatin network becomes incon- 
spicuous, the membrane grows thinner and finally dissolves, so that 
the nuclear contents mingle with the cytoplasm. Or, before the dis- 
solution of the nuclear membrane, the network fades away, but large 
nucleolus-like globules appear, which after the breaking down of the 
membrane become distributed in the cytoplasm (fig. 134). 
TETRASPORE FORMATION. 
It is probable that true tetraspores are never formed on the sexual 
plants of Polysiphonia. Certain abnormalities will be discussed 
in the next section of this paper. The cell lineage of the tetraspore 
in the Rhodomelaceae was correctly described by FALKENBERG (27). 
HEyDRICH (41, 42) gives an account in which he contends that the 
tetraspores are formed after a nuclear union within the mother cell, 
and that tetraspore formation may be the forerunner of a method of 
sexual reproduction. His studies seem to have been made upon 
unsatisfactory material and without cytological methods, to judge 
from his figures. Since I have not been able to confirm his conclu- 
sions or to establish any relation between them and my own, I shall 
not discuss them further. 
The beginning of tetraspore formation is the development of a 
pericentral cell laterally from the central siphon (fig. 140, pc)- The 
mitosis previous to the formation of the pericentral cell (figs. 136-1 39) 
shows that its nucleus contains 40 chromosomes. The pericentral 
cell then cuts off a cell above (fig. 140, mc), which becomes the tetra- 
spore mother cell, attached by a stalk (fig. 140, sc) to the central 
siphon. 
The formation of the tetraspore mother cell was traced in detail 
through the prophase, metaphase, and anaphase of the nuclear 
division in the pericentral cell (figs. 141-146), and the number of 
chromosomes which enter the tetraspore mother cell is clearly 49: 
