156 



METHODS IN PLANT HISTOLOGY 



6. When the section becomes thin enough, or even before if it be- 

 gins to crack, wash off the powder. 



7. It is usually a good plan to use rather thick balsam for mount- 



Fig. 28. — Sphenophyllum pleurifoliolatum: transverse section of a stem cut from a coal ball of 

 the Upper Carboniferous. Eastman Commercial Ortho film.Wratten E filter (orange), J. Swift and 

 Son 1-inch lens; arc light; exposure, 1 second. Slide by Lomax, negative by Sedgwick. X 19. 



