64 MINNESOTA BOTANICAL STUDIES. 



The thallus proved of interest. Murray considers it an aggre- 

 gate of cells loosely bound by tenacula, comparable to the struc- 

 ture of Struvea. Dr. Schmidtz, of Greifswald, considers it an 

 irregularly branched system, equivalent to a congenital branched 

 Cladophora, or a collection of Valonia-\fae cells. Wille, in 

 Engler and Prantl, compares it to a " thickly branched system " 

 sen s t off from a single layer of cells, which coalesce to form the 

 typical layer. 



The writer would compare the plant body to a primitive, ir- 

 regular, sessile, branched system, homologous to the elongated 

 branched system of Struvea. Each cell may be considered a 

 sessile detached branch, which coheres by haptera, not by 

 incrustation. 



The thallus is of a higher type than Valonia, but suggests it 

 in size and structure of cells, and is also a basal type from 

 which still higher branched forms of Valoniaceae can be de- 

 rived. The thallus is not encrusted. 



Size of thallus. The specimens collected were small on an 

 average. 



Length. Width. Depth. 



Average size, 15 mm. 12 mm. 15 mm. 



Largest size, 35 " 25 " 4 " (minus rhizoids). 



Smallest size, 7 " 5 " n " (with rhizoids). 



Color of thallus. The thalli were of a light transparent 

 green color, sometimes tinged with brown or pink. The rhi- 

 zoids were vivid green in some cases. 



It is possible that the strong green or reddish color is due to 

 the plant being intermixed with such forms as Halimeda or 

 some red algae. 



Comparison with other Valoniacea. Dictyosph&ria might 

 be considered a low type because : 



1. Of the primitive, closely appressed branched system. 



2. Of the well-developed rhizoids. 



HISTOLOGY. 



The five- to six-sided cells on the external surface differ widely 



vin size, some being much enlarged and protruding (PL XV., Fig. 



j). The inner cells and intercellular spaces enlarge toward 



the center, stretching to abnormal dimensions in older plants. 



Cell walls. The cell walls present a fibrillated appearance, 

 due to a varying number of membrane-like layers (never less 



