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A STUDY OF THE DEVELOPMENT OF DUMONTIA 



FILIFORMIS' 



I. The Development of the Tetraspores 



GRACE A. DUNN 

 The Johns Hopkins University, Baltimore, Maryland 



The tetrasporic and sexual plants of Dumontia filiformis were 

 found at South Harpswell, Maine, growing in the tide pools 

 and on the rocks exposed to the surf. This paper presents the 

 results of a study of the development of the asexual plants. 

 The discussion of the occurrence of the plant and of other phases 

 of its development will appear later in the Botanical Gazette. 

 The tetrasporic plants usually branch freely (fig. 1, A), but 

 mature, simple individuals occur occasionally. 



A. THE DISTRIBUTION OF THE TETRASPORANGIA IN THE THALLUS 



The tetraspores are embedded in the wall of the thallus. 

 They can be seen without a lens in plants which do not contain 

 too much phycoerythrin, if they are examined in strong light. 

 The tetraspores are distributed evenly all around the wall of 

 the thallus throughout practically the entire length of the 

 branches and the main axis (fig. I, B). In all plants, the more 

 mature tetraspores are found in the upper portion of the branch 

 or main axis and the younger ones toward the base. 



B. THE ORIGIN AND STRUCTURE OF THE MOTHER CELL OF THE 



TETRASPORANGimi 



The mother cell of the tetrasporangium is endogenous in 

 origin. Each cell of a primary subcortical branch often pro- 

 duces a mother cell of a tetrasporangium (fig. 1, C). The 

 cells of secondary subcortical branches may also occasionally 



1 Botanical Contribution from the Johns Hopkins University, No. 50. 



271 



