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Squid Seven <testsubject@xxxxxxxxxxxxxx> wrote in
news:SuednZTP3M6pyYjeRVn-2g@xxxxxxxxxxxx:
> I saw pictures about a decade ago of cacti covered in bright
> patterns. I thought I remembered the caption of these pictures
> indicating that these were photographs taken using film sensitive
> to frequencies either slightly higher or slightly lower than what
> humans can see - but frequencies that are visible to many
> nocturnal pollinators. Recently I was reminded of this vague
> memory, and tried to find relevant info on the web. I can't! Am
> I misremembering something, or was I possibly hoaxed? The
> pictures were on the pages of a book I randomly pulled off the
> shelf in a bookstore. It seems to me like a not unrealistic
> evolutionary advantage - what we see as green cacti their
> nighttime pollinators see in shades and patterns intended to
> attract and guide to flowers.
>
> Can anybody help me out here? I did find refs regarding the
> colors of cacti flowers being those most visible at night, but
> nothing regarding uv or infrared. And which of those would be
> more advantageous for critters using moonlight and starlight? My
> instinct says UV, but it's been a decade since I had physics
> 101...
>
> Thanks from a well-rounded amateur!
>
>
>
A lot of flowers have lines that show up in UV but not in visible
light. Lines such as those wouldn't be much help for night
pollinated flowers, as there isn't a whole lot of UV light after the
sun goes down. You would need Infra Red light for night time
viewing. Most cactus flowers where I live (New Mexico) close up at
night and reopen in the morning, the few that open at night are
white, which is the color that would be most visible at night.
Sean
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