Phaeophyceae 



187 



good stain. Safranin and gentian-violet are also satisfactory, but 

 care must be taken not to overstain, since Fucus usually stains deeply 

 and rapidly. 



For the cytologist, Fucus might be used as a test object for testing- 

 proficiency in technic, just as Pleurosigma angulatum is used in test- 

 ing an objective. The nuclear divisions in the antheridium are 

 simultaneous, and at the sixth division, which is the last, there are 

 32 mitotic figures, each with 32 chromosomes which split so that 32 

 go to each pole. When you can make a preparation in which these 



Esc\y - ' 







b&&W&>Vtl 



FIG. 46. Dictyota dichotoma: longitudinal section showing apical cells; photo- 

 micrograph from a preparation stained in iron-alum haematoxylin. X167. 



chromosomes can be counted, your technic is adequate for research 

 work in cytology (Fig. 45). 



Dictyota. Dictyota deserves a place in the series illustrating the 

 evolution of sex, since its large egg has lost all motility, but the 

 difference in size of egg and sperm is not so extreme as in Fucus. 

 It also furnishes an excellent example of the development of a thallus 

 from an apical cell (Fig. 46). 



Mount habit material on paper. For sections, fix in chromo- 

 acetic acid. For figures, cut 3 to 5 ju, but for general views of apical 

 cell and reproductive phases, cut 10 p. Stain in iron-haematoxylin 

 and counter-stain for 2 or 3 minutes in safranin. 



