Leftwood said:I'll have to ruminate some more about the expectation of the errant white needing to be through to the backs of the petals to signify a virus; the layers of cells from top to bottom(or front to back) are not homogenous, so I don't think I would dictate that viral reactions would be homogenous throughout. Notice, for example, that the spots in the same areas seem not to be affected at all. Looking back over some other pics I have of virused flowers, this seems to be a common trait. But to be a blemish as Lorn describes, he is right that it would not affect the petal backs.
Here are some pictures that I think illustrate what Rick is talking about. There are areas where the errant white will not go through, particularly those areas of heavy or varying petal substance such as mid ribs and mid rib farrows, spots and papillae. These pictures are of two different flowers, and there are two pictures of each flower showing the face and reverse of each, with specific 'landmark' blocked areas to look at. Disregard the rips and tears; those are from last summer's mysterious bird attack. If you look at the face views, you can see long streaks of color blocking running along each side of the rib farrow, but no blocking on the farrow itself. Looking at the same feature on the reverse, one can see the mid rib and areas immediately next to it are not blocked all the way through. These are areas of heavy or increasing substance. Now, examining the sepals feature, one can see a dominant block on the face view of each flower. Examining the reverses, one can easily identify the same block showing all the way through. These are areas of fairly constant petal substance. So, color blocking need not go all the way through to signal TBV, but it's a sure sign if it does.
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