The main device (symbol) in the Plot blazon is the quatrefoil. The main tincture (color) is vert.
The deep green colour that is so often observed in heraldry is more properly known as vert. According to Wade, the use of this colour signifies “Hope and Joy”, but may also represent, rather delightfully, “Loyalty in Love” 1The Symbolisms of Heraldry, W. Cecil Wade, George Redway, London, 1898 P36. It has other names also, the French call it sinople, perhaps after a town in Asia Minor from where the best green die materials could be found 2A Glossary of Terms used in British Heraldry, J.H. Parker, Oxford, 1894, Entry:Vert. More fanciful heralds liked to associate it with the planet venus and the precious stone emerald 3Boutell’s Heraldry, J.P. Brooke-Little, Warne, (revised Edition) London 1970, P 27. More strangely, there is some evidence that the term prasin was anciently used, being the Greek for the vegetable we call the Leek!
Natural objects abound in heraldry, and one category that gives especial delight are the many flowers and flowering plants that frequently occur 4A Complete Guide to Heraldry, A.C. Fox-Davies, Bonanza (re-print of 1909 Edition), New York, 1978, P262. Like its close heraldic relative the cinquefoil, the quatrefoil is a rather sytlised flower showing four rounded petals, usually pierced by a circle at the centre.