// Twitter Cards // Prexisting Head The Biologist Is In: Rainbow Rose

Friday, December 27, 2013

Rainbow Rose

As children, many people colored white carnations by putting food coloring into the water used to keep the flower fresh.   The technique to make rainbow roses is just a couple steps past those carnations.

The process works because a cut-flower is alive and constantly soaking up water to fuel its metabolism.   Much of the stem is filled with cells specialized to transfer water (and anything dissolved in that water) up (and down) the stem.   Moisture is constantly evaporating from the surfaces of leaves/petals and the force of this pulls water up from the roots (or vase).   The water transporting tissues aren't perfect and there is some diffusion of fluids across the width of the stem, but it is much slower than the fluid travel along the stem.

The base of each petal is fed from a small portion of the stem, including only a small amount of the fluid transporting tissues.   Because the dye is added to a specific arc of the stem and diffuses slowly around it, each petal will end up with a different amount of each dye.

As each petal grows to be much wider than its base, the color it acquired is spread around the arc of the flower to result in the lovely mismatch of colors seen between adjacent petals.



The angle between two adjacent petals around the flower approximates 137.51°, which is the smaller angle generated when the average ratio of adjacent Fibonacci numbers is applied to a circle.   The Fibonacci sequence is generated with a simple formula (ni=ni-1+ni-2; n1=1; n2=1) and just happens to match the arrangement of petals around a flower because it corresponds with the most efficient packing of petal primodia into the limited space of the flower primordium.

You can make your own rainbow roses from a white rose and different food colors.   The process is patented, providing legal protection for the one commercial supplier.



There are numerous vendors on Ebay/Amazon/etc. selling seeds for unrealistically spectacular roses, including a rainbow-rose using the image at right.   Modern roses are the result of centuries of hybridization, resulting in a complex mix of heterozygous alleles for many genes.   This high degree of heterozygosity means that the only way to propagate a specific rose variety is to make (clonal) divisions. Seed grown from a rose will generally not be like the parent plant.   (Wild roses are the exception, as they are relatively genetically homogenous within each species.)

It happens to be that this particular rainbow-rose was created on a computer.   I found the original was a stock photo from GettyImages.   Other rainbow-rose seed sale offers will likely have photos of the real, manufactured, rainbow rose.

It takes several years to grow a rose plant from seed to its first flower.   You will have no recourse with the online markets for when you realize the seed you purchased did not grow into what you were told they would grow into.