Publisher Summary This chapter discusses the interactions and internal programmes that result in the patterned differentiation of vascular tissues. The term “pattern” is used to refer to the high degree of order, or predictability, of the system at all levels— the orientation and contacts of the strands forming a coherent system supplying all the organs of the plant, the organization of the transporting cells in files that are functional vessels and sieve tubes, and the relations among the different vascular tissues (phloem, cambium and xylem) and their component cells. The stress is, thus, on relations between cells of the same and of different types and not on the processes of differentiation and controlled gene expression. It is shown that all aspects of the development and maintenance of the vascular tissues might depend on one control system, which is at least partially hormonal. The way this control could operate is in the working hypothesis that together with the problems and possibilities it poses is the central conclusion of this work. A major characteristic of the hypothesis considered is that a gradual, feedback relation between differentiation and signal distribution creates a reliable pattern. Controls of this type may not result in very precise patterns, but they would be simple and dependable in avoiding mistakes of functional significance. They could, thus, account for the vascular patterns found in plants, where no two halves of the same leaf are exactly the same. These controls also have the virtue of depending on known signals and cellular responses. It is, thus, possible that the principles on which these controls are based have a wide relevance, both in plants and in other cases of biological development. The results considered in the chapter suggest that plant hormones, and especially auxin, play an essential role both in the relation among plant organs and in the relations among neighboring cells.

The Control of the Patterned Differentiation of Vascular Tissues

COMPARATIVE EMBRYOLOGY OF ANGIOSPERMS is a review of thedevelopmental processes leading to sexual reproduction inflowering plants. On the basis of embryological data andcertain evidences from other areas of study, it lays specialemphasis on the relationship among and within the familiesand orders of angiosperms. Occasionally, inaccuracies inobservation and interpretation are pointed out, alternativeinterpretations offered, gaps in our knowledge highlighted,and prospects outlined. The text is documented with 36tables, 376 figures, and about 5000 literature citations,which contribute to making this book comprehensive. Besidesstudents and research workers interested in angiospermembyology, taxonomists, plant breeders, agriculturists, andhorticulturists will also find much useful information inthis treatise.

Comparative Embryology of Angiosperms

Ehrlich and Raven's postulate that rapid diversification follows innovation in plant defense has often been invoked a posteriori for plant lineages of unusual diversity and chemical distinctiveness. The postulate can be more rigorously tested by defining a novel class of defense using chemical and/or anatomical criteria, independent of taxonomic lineage. If multiple plant lineages have evolved the new defense type, then according to the postulate they should be consistently more diverse than their sister groups (of equal age, by definition) when the latter retain the primitive defensive repertoire. Secretory canals are an independently defined, repeat- edly evolved feature that functions to protect plants from herbivores and pathogens. The canals might therefore be expected to allow plant radiation in an adaptive zone of reduced herbivory and disease. We have quantified the evidence for this hypothesis by comparing the diversities of lineages that have independently evolved canal systems with their sister groups for as many plant lineages as current taxonomic evidence allows. A sign test showed that canal-bearing lineages have consistently higher diversities than their sister groups (P = .0021). Explanations for this result, other than selective advantage conferred by secretory canals, are examined and provisionally rejected.

Escalation of plant defense: do latex and resin canals spur plant diversification?

Many plants take up soluble monosilicic acid from the soil. Some of these plants subsequently deposit it as cell inclusions of characteristic structure. This article describes the distribution and diversity of opaline silica bodies in monocotyledons in a phylogenetic framework, together with a review of techniques used for their examination, and the ecology, function and economic applications of these cell inclusions. There are several different morphological forms of silica in monocot tissues, and the number of silica bodies per cell may also vary. The most common type is the “druse-like” spherical body, of which there is normally a single body per cell, more in some cases. Other forms include the conical type and an amorphous, fragmentary type (silica sand). Silica bodies are most commonly found either in the epidermis (e.g., in grasses, commelinas and sedges) or in the sheath cells of vascular bundles (e.g., in palms, bananas and orchids). Silica-bearing cells are most commonly associated either with subepidermal sclerenchyma or bundle-sheath sclerenchyma. Silica bodies are found only in orchids and commelinids, not in other lilioid or basal monocots. In orchids, silica bodies are entirely absent from subfamilies Vanilloideae and Orchidoideae and most Epidendroideae but present in some Cypripedioideae and in the putatively basal orchid subfamily Apostasioideae. Among commelinid monocots, silica bodies are present in all palms, Dasypogonaceae and Zingiberales but present or absent in different taxa of Poales and Commelinales, with at least four separate losses of silica bodies in Poales.

Margaret Y. Stant

Papers

Anatomy of the Alismataceae

The Shoot Apex of Some Monocotyledons

Anatomy of the Butomaceae

The Effect of Gibberellic Acid on Fibre-cell Length

Scanning electron microscopy of silica bodies and other epidermal features in Gibasis (Tradescantia) leaf