In a compatible pollination in Crocus, pollen tube tips enter the stigma papillae after the enzymic erosion of the cuticle, and the tubes continue downward growth towards the ovary between the cuticle and the underlying pectocellulosic wall. The cuticle of the receptive zone of the stigma papilla is chambered, the chambers containing a secretion accumulated during the maturation of the stigma. Pollen exudates contain various acid hydrolases, but are incapable alone of eroding stigma cutin. Furthermore, there is no penetration when the proteins of the wall-held stigma secretions are degraded enzymically. These facts are taken to indicate that the pollen contributes a ‘cutinase’ precursor which is activated by a factor or factors held in the stigma secretion. Pollens of certain Cruciferae produce tubes capable of penetrating the Crocus stigma cuticle, suggesting that notwithstanding the taxonomic remoteness of Cruciferae and Iridaceae the enzyme activation systems are quite similar.