Name the lid-like structure found over moss capsule
Answers
Where a seta is present it elongates early, while the spore capsule is still undeveloped, and the elongation is by production of additional cells. In a species with a long seta the growing sporophyte breaks through the enveloping calyptra. The lower part of the calyptra is left around the base of the seta and the calyptra's upper part is carried aloft, still covering the undeveloped spore capsule. You can see an immature sporophyte in the centre of this photo click for photo of Papillaria zeloflexicaulis. The seta has expanded and there is both a basal calyptral remnant as well as one over the apex of the sporophyte. In this species the calyptra is clearly rather hairy. By contrast, the calyptra of Encalypta vulgaris click for photo is smooth. The upper part of the calyptra will eventually become loose and will fall off the capsule as it gets close to maturity. This photo click for photo shows a still green but well-expanded spore capsule of Pleurophascum grandiglobum. The brown, triangular piece of tissue sitting on the capsule is the upper calyptral remnant, quite loose by now.
The seta of an immature sporophyte is not fairly straight in all species. That the seta can be twisted is shown by Funaria hygrometrica click for photo and even more so by Campylopus introflexus click for photo. In the latter the immature setae are so contorted that the young spore capsules are held down amongst the leaves of the cushion composed of massed gametophyte plants. It is only near sporophyte maturity that the seta uncoils and raises the spore capsule above the moss cushion. In order to take that photograph of immature Campylopus introflexus sporophytes the moss cushion had to be teased open a little, and some plants removed, in order to reveal the spore capsules.
The early stage of sporophyte development, where there is a seta, is often referred to as the spear stage because the undeveloped spore capsule typically shows, at most, as a slight thickening at the top of the seta and so resembles a spearhead on a spear shaft. The spore capsule will mature and enlarge atop the seta. The seta and immature capsule in the young sporophyte are both green and contain photosynthesizing cells but the sporophyte is still heavily reliant on nutrients passing to it from the gametophyte. A study into photosynthetic activity of the spore capsules of three moss species showed that the photosynthesizing capsule of Funaria hygrometrica contributes about 50% of its nutrition needs during the later stage of capsule expansion. For the species Mnium hornum the figure is about 20% and for Pleuridium acuminatum it is about 10%reference link.
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Macromitrium with sporophytes
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Peristome teeth on moss spore capsule
The sporophyte eventually stops photosynthesis and the capsule turns brown late in sporophyte development, as does the seta if present. Here click for photo is a colony of a species in the genus Bryum in which all the spore capsules are still immature. Amongst the setae some are green and some are already brown. It is common to see sporophytes in various stages of development. In this photo (right) of a plant of the genus Macromitrium there is one immature sporophyte, still within a yellowish, fibrous calyptra, as well as two fully mature sporophytes.
In a species with no seta, or just a very short seta, it is the enlarging capsule that ruptures the calyptra. The sporophyte of Goniomitrium acuminatum click for photo has a very short seta. The photo shows some enlarged but still green spore capsules, each within the distinctive 8-pleated calyptra of this species.