59 



length of the cells in the thicker part of the filament varies 

 from about V3 of the breadth to as much as the breadth. The 

 basal cell of young- filaments is elongated, and either of the 

 same thickness all over, or tapering towards the base. As the 

 plants grow older the base 

 of the basal cell is enlarged 

 into a kind of basal disc, of 

 the shape of a watch-glass, 

 turning its concave side to- 

 wards its substratum, the 

 branches of AcrosipJionia ; 

 the margin of this basal disc 

 is either entire or lobed or 

 even palmate. The disc, or 

 the discoidally enlarged base 

 of the basal cell , is very 

 distinctly marked from the 

 upper part of the basal cell. 



The part of the basal cell " ^^e filament has been removed from 



the substratum, the discoidally widened 

 lower end of the basal cell is unilater- 

 ally developed, and we look from below 

 into the lumen of the cell, a 277 : 1 : 

 b 667 : 1 . 



c, a fragment of a filament showing 

 the imperfectly divided zoosporangia. 

 422: 1. 



d, a fragment showing the shape of 

 the chromatophore and the position of 

 the single pyrenoid. 422: 1. 



e, a single articulation (compare the 

 text) composed of 4 cells, showing the 

 shape of the chromatophore and the 

 position of the single pyrenoid. 667 : 1. 



Fig. 9. Ulothrix scutata nov. spec. 



a, b, The inferior part of two filaments 



showing the narrower basal portion and 



the lower portion of the thicker superior 



part, besides the lobed basal cell, hi 



which is next to the disc is 



often distinctly constricted, 



has thick walls and narrow 



lumen. Rhizoids are frequent, 



both extramatrical even in 



young plants, and intramatrical 



especially in older plants, but 



the filaments are not rarely 



destitute of rhizoids. The cell 



only contains a single, lateral 



nucleus. The chromatophore 



is belt-shaped and does not fill the length of the cell : 



it contains a single lateral pyrenoid in its broader and 



thicker end. 



I have not met with specimens with fully ripe sporangia, 



