The very different evolutionary pathways of conifers and angiosperms are very informative precisely because their wood anatomy is so different. New information from anatomy, comparative wood physiology, and comparative ultrastructure can be combined to provide evidence for the role of axial and ray parenchyma in the two groups. Gnetales, which are essentially conifers with vessels, have evolved parallel to angiosperms and show us the value of multiseriate rays and axial parenchyma in a vessel-bearing wood. Gnetales also force us to re-examine optimum anatomical solutions to conduction in vesselless gymnosperms. Axial parenchyma in vessel-bearing woods has diversified to take prominent roles in storage of water and carbohydrates as well as maintenance of conduction in vessels. Axial parenchyma, along with other modifications, has superseded scalariform perforation plates as a safety mechanism and permitted angiosperms to succeed in more seasonal habitats. This diversification has required connection to rays, which have concomitantly become larger and more diverse, acting as pathways for photosynthate passage and storage. Modes of growth such as rapid flushing, vernal leafing-out, drought deciduousness and support of large leaf surfaces become possible, advantaging angiosperms over conifers in various ways. Prominent tracheid-ray pitting (conifers) and axial parenchyma/ray pitting to vessels (angiosperms) are evidence of release of photosynthates into conductive cells; in angiosperms, this system has permitted vessels to survive hydrologic stresses and function in more seasonal habitats. Flow in ray and axial parenchyma cells, suggested by greater length/width ratios of component cells, is confirmed by pitting on end walls of elongate cells: pits are greater in area, more densely placed, and are often bordered. Bordered pit areas and densities on living cells, like those on tracheids and vessels, represent maximal contact areas between cells while minimizing loss of wall strength. Storage cells in rays can be distinguished from flow cells by size and shape, by fewer and smaller pits and by contents. By lacking secondary walls, the entire surfaces of phloem ray and axial phloem parenchyma become conducting areas across which sugars can be translocated. The intercontinuous network of axial parenchyma and ray parenchyma in woods is confirmed; there are no “isolated” living cells in wood when three-dimensional studies are made. Water storage in living cells is reported anatomically and also in the form of percentile quantitative data which reveal degrees and kinds of succulence in angiosperm woods, and norms for “typically woody” species. The diversity in angiosperm axial and ray parenchyma is presented as a series of probable optimal solutions to diverse types of ecology, growth form, and physiology. The numerous homoplasies in these anatomical modes are seen as the informative results of natural experiments and should be considered as evidence along with experimental evidence. Elliptical shape of rays seems governed by mechanical considerations; unusually long (vertically) rays represent a tradeoff in favor of flexibility versus strength. Protracted juvenilism (paedomorphosis) features redirection of flow from horizontal to vertical by means of rays composed predominantly or wholly of upright cells, and the reasons for this anatomical strategy are sought. Protracted juvenilism, still little appreciated, occurs in a sizeable proportion of the world’s plants and is a major source of angiosperm diversification.

中文翻译：

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木材中的活细胞 3. 概述；实质网络的功能解剖

针叶树和被子植物非常不同的进化途径提供了非常丰富的信息，正是因为它们的木材解剖结构如此不同。来自解剖学、比较木材生理学和比较超微结构的新信息可以结合起来，为轴向和射线薄壁组织在两组中的作用提供证据。Gnetales 本质上是带有血管的针叶树，与被子植物平行进化，向我们展示了带血管的木材中多列射线和轴向薄壁组织的价值。Gnetales 还迫使我们重新审视无血管裸子植物传导的最佳解剖学解决方案。含血管木材中的轴向薄壁组织已经多样化，在储存水和碳水化合物以及维持血管传导方面发挥着突出的作用。轴向薄壁组织，连同其他修饰，已经取代了鳞状穿孔板作为一种安全机制，并允许被子植物在更具季节性的栖息地中取得成功。这种多样化需要与射线相联系，射线随之变得更大、更多样化，充当光合产物通过和储存的途径。生长模式，如快速冲刷、春季长叶、干旱落叶和支持大叶表面成为可能，以各种方式使被子植物优于针叶树。显着的管胞射线凹坑（针叶树）和轴向薄壁组织/射线对血管（被子植物）的凹坑是光合产物释放到传导细胞中的证据；在被子植物中，该系统允许船只在水文压力下存活并在更具季节性的栖息地中发挥作用。在射线和轴向薄壁细胞中流动，由组成细胞的更大的长/宽比表明，细长细胞的端壁上的凹坑证实了这一点：凹坑的面积更大，放置得更密集，并且通常有边界。活细胞上的边界坑区域和密度，如管胞和血管上的那些，代表细胞之间的最大接触面积，同时最大限度地减少壁强度的损失。可以通过尺寸和形状、更少和更小的凹坑以及内容物将射线中的存储单元与流动单元区分开来。由于没有次生壁，韧皮部射线和轴向韧皮部薄壁组织的整个表面成为糖可以转移的传导区域。证实了木材中轴向薄壁组织和射线薄壁组织的连续网络；进行三维研究时，木材中没有“孤立的”活细胞。活细胞中的水储存以解剖学和百分位定量数据的形式报告，这些数据揭示了被子植物木材中多汁的程度和种类，以及“典型木本”物种的规范。被子植物轴向和射线薄壁组织的多样性被呈现为针对不同类型的生态学、生长形式和生理学的一系列可能的最佳解决方案。这些解剖模式中的众多同质性被视为自然实验的信息结果，应与实验证据一起视为证据。光线的椭圆形状似乎受机械因素的影响；异常长（垂直）的射线代表了有利于柔韧性与强度的权衡。长期幼年期（幼年期）的特点是通过主要或完全由直立细胞组成的射线将血流从水平方向重定向到垂直方向，并寻找这种解剖策略的原因。世界上相当大比例的植物中出现了长期幼稚现象，并且是被子植物多样化的一个主要来源，但仍然很少受到重视。