iy, 
19. Ceramium rubrum, J. Ag. 
Ceranuum rubrum was the subject of a special study 
extending over two years from which valuable data was 
collected bearing on periodicity of reproduction. The 
plant is a common component of pools in the littoral zone 
from about half-tide level downwards but specimens 
attain their maximum size in the sub-littoral zone, as an 
examination of cast-up material will readily shew. 
An analysis of the records shews that periodicity in 
reproduction is well marked for this plant. Large 
numbers were collected and examined. In January, 
February and March it was found that 20 per cent. of the 
plants were sterile, 30 per cent. bore tetraspores, and 50 
per cent. were sexual with antheridia- and carpogonia- 
bearing plants in approximately equal proportions. From 
May to August cystocarpic material was abundant and 
predominated over the tetrasporic plants, but during the 
autumn the proportion of tetrasporic plants rose to 50 
per cent. During the early winter months, November and 
December, the tetrasporic plants far outnumber the sexual 
plants. The periodicity is thus clearly marked, giving a 
preponderance of tetrasporic plants in the winter and an 
overwhelming majority of cystocarpic plants in the 
summer, but in neither case is the line of demarcation 
absolutely clearly cut, since tetrasporic plants persist into 
the early summer and cystocarpic plants are occasionally 
found in the winter. 
The results obtained from a study of Ceramium rubrum 
thus confirm the view expressed in text books that winter 
is the period of tetraspore production for the Rhodophyceae 
and that sexually produced cystocarps are characteristic 
of the summer. This cycle by no means holds for all 
Rhodophyceae. For example, Polysiphonia Brodiaer 
shews a complete inversion of this rhythm. The majority 
of the autumn plants shew tetraspores while a few 
