After browsing Sam Bosanquet's piece on Orthotricha I was interested in observing stomata on the capsules of an Orthotrichum, out of curiosity apart from anything else. At the weekend I had seen one dissected, which I think was O.pulchellum, and I could see the immersed stoma which could be seen down a hole in amongst differently shaped cells which pointed the way to it like paving slabs around a small flowerbed.
Last night I carved up an Orthotrichum, and found several stomata around the base of the capsule principally (were they all below, and uncovered by, the calyptra? I now wonder).
This is what I came up with.
Same hole, different camera and lighting:
I think it's immersed because basically I can't see the stoma. It's inside that hole. I'm also embarassed to confess that I 'm not sure which species this is from although I suspect O.rivulare. This is doubly embarassing if true because it ought to be in my herbarium and not on the slab. Well, you live and learn. I still have a bit left so I can make sure. Now I think about it, it could have been diaphanum. Anyway, it shouldn't be too hard to pick up O.affine for comparison - it has superficial stomata.
Here's the link to the article: Bosanquet