When carbon-assimilation is active, starch-granules crowd upon the surface of the pyrenoid and completely obscure it from view.
Sometimes several pyrenoids occur in each chloroplast, as in Mesocarpus and Spirogyra; sometimes only an occasional chloroplast contains pyrenoid at all, as in Cladophora.
They are composed of a homogeneous proteid substance, and often contain albuminoid or proteid crystals of the same kind as those which form the pyrenoid.
Chlamydomonas sp., unicellular; chr.,chromatophore; p.,pyrenoid; H.
The pyrenoid seems to be of proteid nature and gelatinous consistency, and to arise as a new formation or by division of pre-existing pyrenoids.
pyrenoid structure remains elusive, whether formed from a starch sheath and/or proteinaceous layer, and there are as yet few molecular markers.
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