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 

 Galaxaiira 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 



^ Structural dimorphism 01 sexual and tetrasporic plants of Galaxaura obtusata. 

 Biill. Torrey Club 43: 621-624. "o Ja 1917. 



2 Kjellman, F. R. Om Floride-slagtet Galaxaura, dess organografi och sys- 

 tematik. Kongl. Sv. V'et.-Akad. Handl. 33': 1-109. pi. 1-26. 1900. 



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