92 BOTANICAL GAZETTE [AUGUST 
however, it gradually decreases in size, and at the approach of the 
resting stage of the nuclei it becomes unrecognizable. With the 
return of the period of nuclear division, the centrosome-like bodies 
reappear, as just described, at the opposite poles of the nucleus. 
SWINGLE and others who studied Sphacelaria and Stypocaulon 
maintain that the centrosome or “central body” persists from one 
mitosis to another. Harper appears to be of the same opinion, 
as a result of his work on Lachnea and Phyllactinia. As regards 
_ Corallina, the two centrosome-like bodies appear for the first time 
at the period of nuclear division, and gradually disappear with the 
formation of the daughter nuclei. Thus these structures are not 
permanent organs of the cell, but arise de novo at each mitosis to 
carry on the mechanism of nuclear division. 
Formation of tetraspores 
By normal cell division the disk cell divides into two portions, 
the upper portion becoming the tetraspore mother cell, while the 
lower portion becomes the stalk cell. The tetraspore mother cell 
in its growth assumes a clavate form, while its nucleus increases in 
size. At first the structure of the nucleus appears to be the same 
as that of the vegetative nucleus, but by the time the conceptacle 
has developed sufficiently to be recognized as such, the nucleus of 
the tetraspore mother cell enters upon the stage of synapsis. In 
Corallina the chromatin material is so scanty that a continuous 
spireme cannot be formed, but remains in two groups of small 
granules at the poles of the nucleus. When the synaptic period 
has passed, a centrosome-like body appears at each pole. In the 
metaphase a group of twenty-four bivalent chromosomes becomes 
arranged in an equatorial plate, and the paired chromosomes split 
longitudinally and separate into two groups. The first nuclear 
division, which is the heterotypic division, is soon followed by the 
second, or homotypic division. With the completion of the second 
division, there are formed four nuclei within the tetraspore mother 
cell, each of which possesses twenty-four univalent chromosomes. 
Later the tetraspore mother cell, by means of three cleavage fur- 
rows, becomes divided into four portions, each of which develops 
into a tetraspore containing one nucleus. The tetraspores then 
