574 
The attachment disc increases in diameter by marginal growth (comp. KILLIAN 
1926, p. 206), but the thickness increases too by continued apical growth of the 
vertical cell-rows of which it is composed. The large disc mentioned above showed 
a horizontal zonation, evidencing the periodicity of the growth. The number of 
the layers was not always easy to ascertain, because the limits between the layers 
were often indistinct and sometimes confluent, much as in the cortex of Ahnfeltia 
(comp. p. 559); at least 4 or 5 layers could be distinguished. 
The reproduction of Rhodymenia palmata is remarkable by the fact that 
tetrasporangia and antheridia have long been known while female sex organs and 
cystocarps have hitherto been searched for in vain. 
The tetrasporangia are produced in irregular patches on both sides of the 
frond; they arise from superficial cells, being early cut off from a stalk-cell, which 
remains short, while the surrounding sterile cells divide by transverse walls, forming 
short cell-rows which make up the greater part of the sori (comp. Kürtzıng, 1843, 
Taf. 46 1). The sporangia are cruciately divided. The development and the cytology 
have been carefully examined by Miss M. A. WESTBROOK (1928). Reference is made 
to this publication for details, the principal facts only will be related here. In the 
prophase of the first division of the tetrasporangium a double spireme stage and 
a synizesis were ascerlained, and although this occurrence “is not absolute proof of 
meiosis, the constant association of the three in the sporangia of other Florideae 
‘suggests that in Rhodymenia too chromosome reduction is effected” (p. 164). The 
number of chromosomes could not, however, be determined with certainty, and 
the reduction division is therefore not quite settled. In the cortical cells, the number 
of chromosomes was judged to be greater than twenty. 
The ripe tetraspores, according to WESTBROOK, contain numerous starch grains, 
small discoid plastids and an inconspicuous central nucleus. 
The sori arise in the fronds or frond-segments which have been produced 
the winter before. 
The development of the sori probably begins in autumn, for ripe tetrasporangia 
occur in winter (January to April). But the first stages of the sori were not observed 
by me. In the fertile specimens gathered in March and April, the sporangia were 
to a great extent exhausted. It seems that the tetraspore-bearing parts of the fronds 
normally die after the dissemination of the spores. Sori are therefore not to be found 
in summer and early autumn; in two cases only emptied sori were still met with 
in July (Bw) and September (Ks). 
At more northern coasts the occurrence of the tetrasporangia is not limited to 
the winter, for at Iceland (Jönsson) and in Trondhjem Fjord (Printz) they may 
be met with the whole year, and at the isles of Færûe they were met with in April, 
May, June and November (BoRGESEN), while at the coasts of England and France 
(Cherbourg) they only occur in winter. 
The antheridia form patches on both sides of the frond similar to the tetra- 
sporic sori but of a paler colour. They were first mentioned and figured by THYRET 
