Pelargonium transparent leaf spots

[CallMeDave4]

Hello,

My pelargoniums have developed many pinprick transparent spots on the leaves. They are only obvious when daylight is shining through the leaves. The plants have been inside since autumn. No spots were apparent when I brought them in. There are 4 plants sitting next to each other and they all seem to have it to varying degrees.
Any idea what this is? Would cutting off the affected parts stop the spread to the rest of the plant? Or would I need to propagate new plants from clean looking growing tips?

Thanks for any advice.

 

[Marck]

Greetings, welcome to the Forums.

Interesting, what do the leaves look like with typical, reflected light. You say the spots are not obvious, but there may be some difference in texture or color. Do have a hand-lens to examine the spots in detail?

 

[CallMeDave4]

Thanks for the response.
With dull reflected light the leaves look essentially normal. See photo. This is a leaf which is very 'spotty' when viewed with transmitted light.
With strong reflected light (sunshine) the spots are noticeable.

There is no change in texture on the surface or underside of the leaves, as far as I can tell. It's as if the internal layers of the leaves are becoming transparent and leaving the outer layers intact.
I have a 200X magnification USB camera which I can use to take a close up. (It's currently at work).