246 METHODS IN PLANT HISTOLOGY 



For your test, don't try to stain a 5 /x section; cut at 2 /i, and if you 

 have a good sliding microtome, try 1 /x. Good ribbons of root-tips have 

 been cut at 0.5 n, in 52° C. paraffin, without icing. The room tempera- 

 ture was — 2° C. 



Dictyota. — Didyota deserves a place in the series illustrating the 

 evolution of sex, since its large egg has lost all motiUty, but the differ- 

 ence 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. 



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 fx. Stain in iron-haematoxyhn and counter- 

 stain for 2 or 3 minutes in safranin. 



