Joe Mertzweiller's hybridizing program was unique.  A chemist by training, Joe developed an interest in the development of tetraploid irises, which involves the doubling of the sets of chromosomes in the plant from two to four.  Some plant groups are naturally tetraploid, but in others (daylilies, for example) this characteristic has been induced, as Joe succeeded in doing in Louisiana irises, by application of the chemical colchizine.  The rationale for producing tetraploid plants rests on the creation of heavier substance in foliage and flowers and on increased possibilities of genetic variation in offspring.

Joe Mertzweiller wrote the book on the development of tetraploid Louisiana irises.  Each individual picture on this page represents one of Joe's tetraploids growing in the Louisiana Iris Garden.  The future of tetraploid Louisianas is unclear, and most hybridizers still work with plants in their natural diploid state.