[Reprinted from BROOKLYN BOTANIC GARDEN MEMoIRS, 1: 191-197. 1918.] 
FURTHER NOTES ON THE STRUCTURAL DI- 
MORPHISM OF SEXUAL AND TETRASPORIC 
PLANTS IN THE GENUS GALAXAURA 
MARSHALL A. HOWE 
The New York Botanical Garden 
At the meeting of the Botanical Society of America, held at Colum- 
bia University in December, 1916, the writer presented a short paper, 
since published,! in which evidence was brought forward to show that 
Galaxaura obtusata, a calcified red alga of the family Chaetangiaceae, 
presents itself in two forms of the same general habit, but differing 
markedly and constantly in the microscopic structure of the cortex. 
In the one, the middle layer of the cortex consists chiefly of large 
chambers, more or less filled with lime in the natural condition, while 
in the other the chambers are comparatively small and the cortex is 
pseudoparenchymatous throughout. There are also other differences 
in the form and relations of the cortex cells, as pointed out in the 
paper to which reference has been made. In a monograph of the 
genus Galaxaura, published by Kjellman in 1900,? these characters 
were made the basis of two groups of species, denominated by him the 
‘“‘Cameratae’’ and the “Spissae.’’ In the recently published paper, 
the present writer drew attention to the facts that plants showing 
the ‘‘Cameratae’”’ and ‘“‘Spissae’’ structure are commonly collected 
together throughout the West Indian~region, that they show the 
same or parallel variations in external habit, that they can not, in 
fact, be separated without a microscopic examination, and that, when- 
ever reproductive organs can be found, the plants of the ‘‘Cameratae’ 
structure are always tetrasporic, while those of the ‘‘Spissae”’ struc- 
ture are always antheridial or cystocarpic. The writer therefore 
expressed the conviction “‘that the ‘Spissae’ and ‘Cameratae’ char- 
acters, first accurately pointed out by Kjellman, do not offer a proper 
basis for subgeneric groupings of species as supposed by him,” but 
merely distinguish the sexual and tetrasporic phases in the life-cycle 
of a single species. 
Since reading and publishing the short paper to which reference 
1 Structural dimorphism o1 sexual and tetrasporic plants of Galaxaura obtusata, 
Bull. Torrey Club 43: 621-624. 10 Ja 1917. 
2 Kjellman, F. R. Om Floridé-slagtet Galaxaura, dess organografi och sys- 
tematik. Kongl. Sv. Vet.-Akad. Handl. ae: I-109, pi. I-26, 1900. 
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