-38- 

 was done at 55-60 C for 12 hours. Ultrathin sections were 

 placed upon Formvar carbon-coated copper grids and exposed 

 to 10% ovalbumin solution for 10 minutes. The excess 

 liquid was then blotted from the grids with filter paper. 

 Following this, grids were floated on a drop of PBS- 

 diluted antiserum (1/500-1/2000) for 30 minutes. Grids were 

 then rinsed 3 times with 20 mM PBS buffer for 10 minutes 

 each and then incubated with protein A-gold for 30 

 minutes. Finally, grids were rinsed with PBS buffer for 

 20 minutes, followed by a 10 minute rinsing in distilled 

 water. The sections were poststained with 2% uranyl 

 acetate and 0.2% lead citrate and examined by electron 

 microscopy. Tissues incubated with normal serum were used 

 as controls for all samples studied. 



Results 



VaMo Negative Staining 



The VaMo negative staining method was very useful for 

 detecting CyMV and ORSV particles in orchid leaf and 

 flower tissues. With this method, most virus particles 

 accumulate at the edge of the staining solution on the 

 grid and appear with good contrast and resolution 

 (Figs. 29, 30 and 32). With the conventional PTA negative 

 staining method, virus particles were not concentrated at 



