Question: Explain Variegation in Ivy (xiii): testing the theory: predicting the yellow centre

I would like to start the test of the theory with the prediction of the yellow centre (according to Zonneveld). After that I will try to explain the white margin and work my way through the more complicated types of variegation: the streaked and speckled patterns. See my other site 'Mere Ivy' (july 1st, 2006) for pictures of my favourite variegated cultivars.

One cell in the L3 layer of the apical meristem mutated and divided so all cells of the layer have the same mutation. Contributed cells of this layer develop albino chloroplasts. Because the L3 layer is responsible for the centre of the leaf, the centre would be white. However, the cells originated from the L2 layer are not mutated and therefore green. The mutated cells are sandwiched between these green cells so the white becomes yellow. Hedera helix 'Goldheart' is a cultivar with this pattern.

There's no word about the cause of the distinct border between the two colours. I think the cause is found in the vertical orientation of palisade cells in the palisade mesophyll. The border between L3 layer cells and L2 layer cells is therefore abrupt and the border between the colours clearly defined.

Source: Variegated trees & shrubs, Ronald Houtman, 2004, Timber Press

Next time I'll try to explain the white-margined variegation, the streaked pattern and the speckled pattern.