They
were fixed overnight at 4 1C in 2.5 percent glutaraldehyde and 0.1 M cacodylate
buffer pH 7.4. In both cases, material was post-fixed for 2 h in one percent osmium
tetroxide and buffer phosphate 0.1 M pH 7.4. The cells were washed three times in
phosphate buffer 0.1 M pH 7.4, dehydrated in acetone series (30 percent, 50
percent, 70 percent, 95 percent, and two of 100 percent) and embedded in Spurr
resin low density (Spurr, 1969). Sections were cut with a diamond knife and stained
with uranyl acetate two percent in aqueous phase for 45 min. and lead citrate five
percent for 5 min