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Re: Phototropism



Dear Marek,

Your comment:

From my experience.
When I buy Cryptocorynes in a shop they have very long petioles
but in my well ligtened aquarium they become very short

This is a different sort of phenomenon than what I am speaking about. Some, perhaps most species in this genus do become very different in leaf morphology when grown under different lighting and planting conditions. The again, sometimes just the opposite happens; the leaves and petioles elongate from what you buy at the store or at an auction. In general, however, Crypt leaves tend to look more like your "before" pictures. My bet is that those had been growing emerse (with leaves into atmosphere), while yours look submerged. That alone is enough to account for how different they look now.

If you look at the right-hand picture of the newly-purchased plants on your site (the ones in the mesh baskets)

http://www.wschowa.com/abrimaal/araceum/cryptocoryne/wendjahn.htm

you will see the sort of situation that can lead to a "flip-over". If that plant were planted in a shallow-immersed situation, where the leaves tend to splay across the water surface, that middle leaf could well end up with its underside exposed to the sky. We are not speaking here of an event where the petiole has folded, kinked, or twisted. Those conditions would obviously result in a physical problem for the conduction of sap containing soluble foodstuffs that could well lead to the plant sacrificing that leaf. But because the petioles tend to be rather flexible in this genus, the chances of ending up with an inverted leaf are good.

Judging from the lack of responses I am thinking that the list does not know the answer. If I think of all the leaves I have ever seen, unless a plant has suffered damage, all the leaves want to be more or less horizontal. There is an upper leaf surface and a lower leaf surface. The upper leaf surface may have a thicker skin, perhaps with a waxy coating, or a darker color to deal with the stress of being in direct light and more exposed to the elements. The underside is specialized by having gas-transport structures, perhaps hairy features, and who knows what else. The leaf may be exactly horizontal or may prefer to orient itself at some angle (up or down from horizontal). Or it may even change as the leaf matures. But this presentation to the world is a characteristic of the plant. And it is always directional in higher plants. Algae and such may be different.

At the same time leaves are typically translucent. This means that if you place a leaf between you and a light source you can detect the light coming right through the tissue. To be sure, some wavelengths have been filtered out, which is why the leaf looks green (or reddish, or brownish, etc.). But the same sort of filter is in place if you look through the other leaf surface. It still looks green, meaning that light has been gathered and filtered. Is light coming up through the leaf underside useful for photosynthesis? If not, why not?

Don't think I'm pressuring anyone for answers. These are just the questions I throw out because they bug me. There are many unexplained phenomena in the world. Sometimes I think there are more mysteries than there are answers. I am curious.

Ted.
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