Olson : OBSERVATIONS ON GIGART1NA. 165 



In the nemathecia the tetraspores stain a deep violet, as also 

 do the contents of the central filaments just below the spores. 

 The rest of the central filaments remain unaffected and the outer 

 cells stain yellowish brown. 



SPECIFIC DESCRIPTION. 



Gigartina sp. und. Fronds purplish-red, distinctly caules- 

 cent, several often springing from the same disc-like holdfast ; 

 18-28 cm. long by 7-10 cm. wide. Stipe somewhat compressed, 

 3.5 to 5 mm. wide by 2-3 mm. thick, gradually widening into 

 the typically cuneate lamina. Young fronds often entire, older 

 ones sparingly branched, branches expanded, never linear or 

 lanceolate. Cystocarps compound, closed, more or less stalked, 

 several generally occurring crowded together on the same pro- 

 liferation ; enclosed within a pericarp; 1-2.5 rnm. in diameter; 

 carpospores numerous, crowded together in more or less definite 

 groups, oval, 12-15 mic. long by 10-12 mic. wide. Tetraspores 

 produced in nemathecia, on both sides of the frond ; nemathecia 

 wart-like, rising 25-37 mic. above the level of the thallus. Tet- 

 raspores oval, more or less angular, 12-20 mic. long by 5~ 10 

 mic. wide. 



METHODS. 



Part of the sections used were cut with the freezing microtome, 

 the rest by hand. The material used had been preserved in 75 

 per cent, alcohol. The effect of imbedding in gelatine pre- 

 pared according to Osterhout's directions was tested. The por- 

 tions to be sectioned were cut in* pieces .5 cm. long and about 

 the same width and placed in the gelatine. This was left for 

 twenty-four hours to allow the gelatine to penetrate the tissues, 

 then removed and placed in a gum arabic solution on the freez- 

 ing chamber. After several trials it was found that sections in- 

 troduced directly into the gum arabic without embedding were 

 as satisfactory as by the longer process. 



Staining. At first water solutions of the stains were used, 

 but it was found that this caused the tissues to swell to such an 

 extent that cells often presented a very unnatural appearance. 

 For example, a cross section of the stipe was obtained in which 

 the cell lumen appeared irregulary star-shaped or was nearly 

 obliterated (Fig. 16, PI. 14). This was then abandoned and 



*Osterhout. Bot. Gaz. 21: 195-201. 1896. 



