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[APD] cuticles etc
Today I looked at a leaf of Anubias barteri var nana and a strand of Crassula vaillantii under a low power microscope and looked for stomatae.
The Crassula which had germinated underwater in nature and had been kept submerged for 3 months had stomatae all over its surface but the largest concentration was near its growing tip.
The Anubias leaf of a plant (which had been submerged for 2 years in a tank) had stomatae on its lower (abaxial) side as expected in a terrestrial plant, and none that I could see on the upper (adaxial)surface. (Floating plants, water lillies etc have stomata on the surface in contact with air, submerged aquatic plant leaves normally have none).
So what can we conclude? Could the Crassula grow as a terrestrial underwater, respiring through its stomata?
It grows only in shallow temporary rainwater pools and cannot adapt different physiologies to rapidly changing water levels. That's maybe why it retains its cuticle and stomatae. Because of this it would grow much slower next to most aquatic plants found in deeper pools. But these can't survive in the shallow pools because they die if it does not rain in a week's time. So the succulent has found a niche few plants can compete with it.
The Anubias is also a slow grower in an aquarium. Maybe this is because it is much like Crassula in its structure. Why else would it retain stomatae? It seems to grow as a terrestrial but submerged, as if it has not realised its underwater! It even flowers underwater with a flower that's obviously terrestrial. Weird but pretty.
The question I would like a definite answer to is: what relevance would stomatae have in a submerged 'terrestrial-type' plant. Am I correct in assuming that they will still function by diffusion of gasses through the air-water surface at the openings, if they do open?
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