Recently at a nursery I saw some nice topiarys made from chicken wire. There was a shrub with tiny leaves
growing inside of the wire. What could it be?

Pamela,
There is a good chance that it was Serissa. This is an evergreen shrub used in warmer climates for a low hedge or as a bonsai tree. A good plant for the beginner bonsai student. It takes shearing well, has either pink or white flowers and could easily be trained to grow through wire and be shaped.

Pamela,
The shrub you saw could have been a boxwood. They are very hardy, conform well to the cutting frame type (chicken wire) topiary and are popular in nearly every state.

My guess would be a variety of boxwood (English, African, Japenese, etc etc) This is what I see most commonly being used. Keep in mind though that there are many differnet plants that could be used. In general you are looking for a relatively compact and dense shrub that readily branches. The other issues to contend with are leaf size and plant growth. In the case of leaf size the size of the cage is the determining factor the smaller the cage the smaller the leaf size needed in order to maintain the shape of the display. In plant selection you have trade offs. For example your box woods, are typically slower growing which means they require less maintenance, but take longer to grow out a cage. Your pine needle type evergreens (ie Diasoma-Austalian Name) on the other hand fill in quicker but require more frequent pruning. Now if you are looking for almost instant results try stuffing the cage with long fiber moss and using Ivy or creeping fig. It will still take some time for the the frame to cover completely but the moss fill frame looks good by itself. I've seen a few displays that used only moss.

Hope this helps

Mark

When you said 'tiny leaves', my first thought was drawf myrtle, Myrtus communis compacta

Here is a link that might be useful: Chris' Topiary Nursery