-37- 

 with the aid of a wooden applicator stick, blotted with 

 filter paper and transferred to an aqueous, non- 

 fluorescing medium (Aqua-mount, Lerner Laboratories, New 

 Haven, Connecticut 06513) placed upon a glass microscope 

 slide. A cover slip was then placed over the mounting 

 medium and the tissues were observed with a Nikon (Nippon 

 Kogaku K. K., Tokyo, Japan) Flu'ophot microscope with epi- 

 illumination capabilities. The interference excitation 

 filter and barrier filter were used. Observations were 

 recorded with an automatic camera using Kodak Ektachrome 

 400 film (Eastman Kodak Co., Rochester, New York). TRITC- 

 conjugated normal serum and heterologous antisera were 

 used for staining infected tissues as controls. Healthy 

 tissues were also studied as controls. 



Protein A-Gold Labelling 



A solution of protein A-gold (containing colloidal 

 gold particles 15 nm in diameter) was passed through a 0.2 /am 

 millipore filter before use. The tissues studied were as 

 follows: CMV-infected Phalaenopsis , BYMV-inf ected pea, 

 ORSV-infected Cattleya , CyMV-inf ected Cymbidium and 

 healthy Cattleya and Cymbidium . These tissues were fixed 

 with 5% glutaraldehyde and dehydrated through an ethanol 

 series (25, 50, 75, 95, 100%), and embedded in LR White 

 resin, medium grade (Polaron Equipment Limited, 

 Hertfordshire, England). Polymerization of LR White resin 



