Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, Iowa 50011-1020 USA;
Am J Bot. 2005 Dec;92(12):1935-41. doi: 10.3732/ajb.92.12.1935.
Oxalate crystals are very common in angiosperms, but few descriptions of their macropattern (crystal types, their tissue distribution, and development) exist. Because unusually large prismatic crystals and druses, are known from pomegranate, we traced the development of crystal macropattern in various-aged leaf samples from a living plant and from herbarium specimens using unstained whole mounts (some bleached and cleared), stained leaf samples, and leaf and stem cross sections. Preparations were viewed with bright-field light microscopy and with crossed polarizers. Prismatics appear first in the subapical mid-mesophyll layer of a leaf 650 μm long. Additional prismatics form basipetally in the enlarging lamina. A preemptive wave of small prismatics appears basipetally in the midrib. Druses form secondarily acropetally in petiole and midrib, while existing lamina prismatics enlarge and new ones develop among them in mid-mesophyll. Prismatics produced early expand vertically, and many eventually extend from epidermis to epidermis. Later-formed prismatics attain intermediate sizes. No crystals form along lamina veins, but in older leaves, druses occur in spongy mesophyll, mostly near major vein junctions. In the stem, druses are restricted to phloem fibers. No phloem fibers occur in the leaf trace or midvein; therefore, petiolar and midrib druses are only in parenchyma, not in phloem.
草酸钙晶体在被子植物中非常常见，但关于其宏观形态（晶体类型、组织分布和发育）的描述却很少。由于石榴中存在异常大的棱柱晶体和晶簇，我们通过对活体植物和标本的不同年龄叶片样本进行未染色的整体 mounts（一些漂白和透明）、染色的叶片样本以及叶片和茎横切片的研究，追踪了晶体宏观形态的发育过程。使用明场显微镜和正交偏光镜观察了制备物。棱柱体首先出现在长 650μm 的叶片的亚顶端中部叶肉层中。在不断增大的叶片中，棱柱体从基部向上形成。中脉中出现了一波先形成的小棱柱体。晶簇在叶柄和中脉中次生地从顶端向基部形成，而现有的叶片棱柱体增大，新的棱柱体在中部叶肉层中发育。早期形成的棱柱体垂直扩展，许多最终从表皮延伸到表皮。后来形成的棱柱体达到中等大小。叶片脉中没有晶体形成，但在较老的叶片中，晶簇出现在海绵组织中，主要出现在大叶脉连接处附近。在茎中，晶簇仅限于韧皮纤维。在叶柄和中脉中没有韧皮纤维；因此，叶柄和中脉中的晶簇仅位于薄壁组织中，而不在韧皮部中。
