Autafluarescence of the pollen wall of <em>Lilium</em> shows a correlative change with its development. When the pollen of Gasteria is injected into the anther of <em>Lilium</em>, it exhibits almost the same characteristics of wall autofluorescence as those of <em>Lilium</em>. Only the last stages of wall development are dissimilar. During this period the pollenkitt sticks to the pollen wall in <em>Lilium</em> only. The conclusion is that in the exine of <em>Gasteria</em> pollen, in contact with the locular fluid of <em>Lilium</em>, polymerization of <em>Lilium</em> sporapollenin occurs instead of a structural addition to the wall. This polymerization is a continuous process during the entire development.