-7- 

 pieces (ca. 0.5 x 3.0 cm) were cut, laid upon glass slides, and 

 gently rubbed with 320 grit sandpaper first and then 600 grit 

 sandpaper (cut into 1x4 cm pieces) to remove the cuticle and 

 permit stain penetration. Using this technique, it was 

 possible to remove enough overlying tissues to reveal the 

 epidermal layers below those being abraded. 2) For thicker- 

 leaved orchids such as Cattleya , tissues were sliced 

 paradermally or longitudinally with razor blades. Paradermal 

 sections were obtained by cutting leaves parallel to the leaf 

 surface (Fig. 1), while longitudinal sections were obtained by 

 inserting leaf tissues in either styrofoam or pith as a support 

 while they were being sectioned. 



The thick-walled tissues infected with ORSV were stained 

 with the O/G combination at room temperature for 10 minutes and 

 then heated at 60 C for another 5 minutes. Leaves with thin- 

 walled cells were stained in the O/G combination at room 

 temperature for 15 minutes. In some instances, CyMV-inf ected 

 tissues were fixed in 5% glutaraldehyde (in 0.1 M sodium 

 phosphate, pH 7.0) for two hours and then rinsed with the same 

 buffer to preserve inclusion fine structure. For the 

 bacilliform viruses, paradermal strips were first treated with 

 either 5% Triton X-100 for 5 minutes or 1% Triton X-100 for 10 

 minutes followed by staining in Azure A at 60 C for 10 minutes. 



Comparable tissues were also examined by electron 

 microscopy to confirm the light microscopic observations. 

 Tissues were fixed for thin sectioning in 5% glutaraldehyde, 



