All bulb fields in Holland are heavely fertilized each year before the bulbs ( tulips narcissi hyacinths) go in That is why they increase in size an number Ben J.M.Zonneveld Institute of Biology,Leiden University, Clusius lab Wassenaarse weg 64, 2333 AL Leiden, The Netherlands Zonneveld@rulbim.Leidenuniv.NL Fax: +31-71-5274999. min temp -10C (15F)