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Petiole Shortening



Dear Wise Ones,

A phenomenon has come to my attention by way of Jim Langhammer, who used to be a contributor to this list. He is a trained botanist and life-long professional fish and reptile keeper and expert. He is well known in the Detroit area (USA) since he is the retired curator of reptiles at our zoo. The reason I point out this biographical material is to emphasize that he is a close observer of the natural world and one whose observations are to be taken seriously.

Mr. Langhammer has an aquarium of 70 gallons capacity in which he has a culture of Cryptocoryne of the cordata complex. This aquarium has been maintained almost undisturbed for a decade or two with this planting and his results have been remarkable. His plants grow luxuriously with total leaf lengths of around 18 inches (46 cm) at maturity, being perhaps two-thirds petiole length and the balance leaf blade. The leaves are a rich color and apparently in the peak of health. Water is changed two or more times per week. The substrate gets no fertilization other than "mulm" from fish wastes. Over the years illumination has been provided by a single cool-white fluorescent bulb, 24-hours a day.

As it happened, a few months back he decided to switch out the cool-white fluorescent with a gro-light type with a different temperature profile. The reason for the change was to enhance the appearance of some characin fishes in the tank, which was successful.

But over the next few weeks after the bulb switch the plants experienced a dramatic contraction in the petiole length. The leaf blade dimensions did not seem to change much, but the overall leaf length is now less than about 10 inches (25 cm). Old leaves have not died and this is not simply the emergence of new leaves adapted to a new illumination regime. The petioles have contracted on the order of 50%, presumably because of a shift in the intensity or color temperature of the illumination. The petioles are not bent or otherwise distorted; just shorter.

The growth habit of the leaves, it should be noted, has changed as well. Under the old regime the leaves tended to strive upward, as if seeking light. With the new light they tend more toward a horizontal leaf blade orientation. This behavior could indicate a trigger associated with light intensity.

The same phenomenon was reported earlier by another Crypt fancier who had received offshoots from the Langhammer clone. But, at that time, we attributed the episode to the usual adjustment problems associated with radical change in culture and we did not have the controlled observation that we have in this case. The other grower was not certain that the leaves were not just new growth, for example.

We see references to plant contractile activities in certain roots (dandelions, daffodils) that serve to pull bulbs or crowns into the soil, and in tendrils, which coil and contract to pull vining plants like cucumbers toward supporting structures.

Has anyone on the list read about or observed such contractile behavior in Aroids, especially in leaves? We wonder, naturally, if a return to the old illumination regime would result in reversal. We wonder what possible physical mechanism could account for shortening on this scale.

And, I might add, we wonder if we are crazy. If you think I'm crazy I won't be offended. Others have made that inference in the past.

Any ideas?

Ted.
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