Transmission in flowers

[Jim Lloyd]

A few things set me thinking about this. I was observing flies feeding on buttercups (the tall ones growing in meadows, greater ranunculus ?) and saw several flies arrive from below the flower, crawling in over the edge rather than flying in from above. I also noted that these flowers grow on long stems often above the general level of grass and other vegetation. So I wondered what the flower looked like to an insect from below - against the sky rather than from above against the grass. I was also reading this paper (Van der Kooi et al 2016) that present an optical model of the flower. This points out that light hitting the flower can either be reflected, absorbed or transmitted. I wondered if the central dark part seen in UV reflected photography of a buttercup was absorbing or transmitting UV.

 

Below are greyscale images of transmitted light in the UV, blue and green band (from left to right). Taken by photographing against a bright sky (I guess there may be some reflected light, but it should be mainly transmitted).

 

The flower looks completely UV dark, which is not that unexpected as the outer parts are highly reflective and the inner parts must be highly absorbing. Of interest is the relative translucency in the green of the UV absorbing areas. This can quite easily be seen when holding the flower up to the light.

 

Has this subject been studied before? Could this be some signal for insects below the flower? Or just a coincidence to do with the flower structure?

 

[Andy Perrin]

In general UV transmission is low for most substances (and the opposite for infrared). That follows from the basic physics of materials, which says that the attenuation coefficient (light absorbed per unit distance into the substance) is inversely proportional to wavelength. So short wavelengths would get absorbed more than longer ones if all else were equal (which it isn't really, but one can still observe the overall effect). This is why shortwave infrared is used by museums to look underneath the surface layers of paint.

[Andrea B.]

Jim, I'm not sure how the blue and green bands were made? Thx.

 

Bjørn Birna and I do try to photograph the abaxial side* of the flower. Although not usually from looking up underneath.

 

*Both of us forget to do it about half the time.

[Jim Lloyd]

Andrea - Visible image white balanced in camera for full sun - then Blue and green made in photoshop from the visible image using the channel mixer - i.e B= 0R + 0G + 100B then desaturated. Re-imported into Lightroom and then adjusted tone using the auto tone control.

 

Not sure if this is the best thing to do; the translucency is obvious in the visible image.

 

[Andrea B.]

I like it as a photograph (although a bit unfocused). The translucency is intriguing.

 

Investigate whether you want greyscale or desaturation when going monochrome?

[Jim Lloyd]

Yes I need to think about greyscale v desaturation

[Andy Perrin]

IR should show even more translucency. Might want to try 850nm? Then it will be automatically grayscale also.

[Jim Lloyd]

I’ll put that on the to-do list ! ;)

[Andrea B.]

That would be a Todo List. Pronounced "toe-doe". ;)

 

I have so many Todo Lists scattered around. I make them to give myself the illusion of being organized. Then I lose them. It's always interesting to find a Todo List months later and compare it to what I have actually accomplished.

[Jim Lloyd]

I just need a round tuit. I have plenty of square tuits, but when I finally get a round tuit all my to-do lists will be complete !

[Andrea B.]

:lol: :P