[From the Bulletin of the Torrey Botanical Club, 43: 621-624. 6 Ja 1917J 



A note on the structural dimorphism of sexual and tetrasporic 

 plants of Galaxaura obtusata 



Marshall 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, 



v/hich, 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 Floride-slagtet Galaxaura, dess organografi och syste- 

 matik. Kongl. Sv. Vet.-Akad. Handl. 33': 1-109. pi. 1-2C. 1900. 



621 



