220 



THE USE OF THE MICROSCOPE 



smeared, at one stroke, by another slide. (The juice from 

 anther tissue is apparently fatal to optimum fixation.) 

 The smears are fixed immediately in chrom-acetie-formalin, 

 mordanted in iron alum for 24 hours, and stained 2 to 3 hours 

 with brazilin. They are then differentiated in iron alum for 

 a few minutes or so, cleared with cedar oil, and mounted in 

 immersion cedar oil under large covers of 0.17-millimeter 



Fig. 24.- — Pollen mother cell of Lilium pardalinum, showing half the pachytene 

 coils, with over a thousand double (or quadruple) chromomeres. Smear fixed 

 and stained as in P'ig. 23. Camera drawing with fluorite objective 100 of 1.3 

 aperture, Bitumi binocular attachment, and eyepiece magnification of 12.5. 



thickness. Such covers permit, bj^ their elasticity, of 

 pressure being applied on a particular cell or group of 

 cells without fracture of the cover. Chromomeres show 

 well under a fluorite 100 objective, of 1.3 aperture, with a 

 full cone of light from a corrected water-immersion con- 

 denser, and Wratten yellow-green film No. 57A. The 

 chromioles composing the ultimate chromomeres can be 

 observed better after pressing sufficiently on the cover-glass 

 with a long-bladed penknife to flatten the cells somewhat 

 (see Fig. 24). 



Buds of Aloe striata, about 5 millimeters long, also show 

 the ultimate chromomeres well, when smears are stained 

 as above and mounted in immersion oil. FriiiUaria 



