A note on the structural dimorphism of sexual and tetrasporic 
plants of Galaxaura obtusata 
MarsHALt A, HOWE 
In a monograph of Galaxaura, a genus of calcified red algae of 
- the family Chaetangiaceae, published by the late Professor Kjell- 
man of Upsala in 1900,* two groups of species, denominated the 
““Cameratae’’ and the ‘‘Spissae,’’ are recognized in the section 
Dichotomaria, the section that includes the West Indian Galaxaura 
obtusata (Ell. & Sol.) Lamour. and its allies. The plants of these 
two groups differ markedly and constantly in the structure of 
the cortex, as may be determined by a microscopic examination, 
particularly after decalcification. In both groups, the cortex 
consists essentially of three layers of cells. In the ‘“‘Cameratae,’’ 
the cells of the outermost or superficial layer are funnel-shaped 
or broadly obconic and are supported by the cylindric, clavate, or 
narrowly funnel-shaped, widely spaced cells of the middle layer, 
which, in turn, spring from the very large firmly united cells of 
the inmost layer; the funnel-shaped superficial cells are in contact 
by their edges only and they arch over large intercellular chambers, 
which are continuous or confluent, being bounded below by the 
large cells of the inmost layer and merely traversed rather than 
bounded by the widely spaced stalk-cells; in other words, the 
single superficial layer constitutes a sort of a roof or outer sheath, 
supported by short pillars. In the “‘Spissae,”” the cells of the 
outermost or superficial layer are hemispheric or saucer-shaped 
and are supported by the ovoid or subglobose, connivent or 
rather close-set cells of the middle layer, which, in turn, rest upon 
the large firmly united cells of the inmost layer; the intercellular 
spaces are comparatively small and instead of obviously extending 
from the superficial layer to the inmost layer they are commonly 
divided into two series or strata by the rounded connivent cells 
of the middle layer. In other words, the middle layer of the 
* Kjellman, F.R. Om Flovidéskigtet Galaraura, dess organografi och syste- 
matik. Kongl. Sv. Vet.-Akad. Handl. 33!: 1-109. pl. 1-26. 1900. 
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