These roots what are they ?
 

Hello,
Been digging in a garden about 18" down and found some long pencil thick
roots running horizontally.. I broke one and its orange/yellow in colour.

Anyone have any ideas what these roots could be ?
The only plants/shrubs in the vicinity are about 5 ft away. These are
paeony, lupins,rhododendrons and rhubarb.

Also there is possibly some unseen bindweed in the area,this pops up
elsewhere in the garden during the Summer.

Martin