Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             chemical compounds
               Class hydrocarbons [CxHy] - compounds consisting of carbon and hydrogen only
                 Class olefins
                   Class alkadienes - unsaturated acyclic hydrocarbons having two double bonds
                     allene [C3H4; CH2=C=CH2]