232 THE USE OF THE MICROSCOPE 



41. Examination of Vessels and Fibers. — Soak thick, 

 longitudinal slices of material, cut with a knife or plane, in a 

 cold mixture of nitric acid and the chlorate of an alkali. 

 When the material is sufficiently loosened, wash and put 

 it in ammonia solution to complete the process. Wash 

 again, and mount in clear agar; or dehydrate, stain with 

 methyl green, and mount in balsam. 



42. Origin of Cell Layers in Embryo. — Open pollinated 

 ovaries of flowers at different stages, and fix ovules in 

 chrom-acetic-formalin. Omit washing in water. Cut 

 longitudinal sections in paraffin. Wash in alcohol. Stain 

 with Mayer's hsemalum, iron-hsematoxylin in 70 per cent 

 alcohol, or iodine gentian-violet. Try Datura, Nicotiana, 

 and Oenothera. Note origin of cell layers in embryo. 



43. Embryos of Fucus. — Put in a hollow slide with sea 

 water some of the green egg cells and some of the yellow 

 sperm cells. Observe without a cover, with the 10 objec- 

 tive, the attraction of the sperm. Put slide in a moist 

 chamber, and embryo plants will form on the glass. Also 

 observe ova and sperm under a cover-glass with a water- 

 immersion objective. Try hybridizing different species of 

 Fucus. 



44. Fertilization of Ferns. — Grow fern spores on moist 

 tile, under a glass cover, in a saucer with dilute culture 

 solution. Put cut segments of prothallia with archegonia, 

 and of others with antheridia, on a slide with water. 

 Cover, and observe with water-immersion objective. Note 

 entry of sperm into canal. Try to observe hybridization 

 of different species of fern. 



45. Bacteria and Spirochaetes. — Obtain material from 

 unbrushed teeth, or from a case of Vincent's angina, or 

 from decaying legumes in water occasionally changed. 

 Observe alive, in thin layer, with special dark-field conden- 

 ser (cardioid or bicentric) , and special oil-immersion ob j ecti ve 

 of about 1.0 aperture. Covers should be 0.17 millimeter 

 thick. Or use corrected water-immersion condenser of 

 about 1.3 aperture, with central stop just large enough 

 for an oil-immersion objective of about 0.85 aperture. Or 



