AN INTRODUCTION TO MORPHOMETRIC CYTOLOGY AND ITS APPLICATION TO BOTANICAL RESEARCH

Morphometric cytology is the study which quantifies dimensions of cells and tissues through the observations of two-dimensional sections. Useful parameters such as volumes, surface areas, numbers of particles, etc. can be determined from sections of plant materials. This paper introduces botanists to the basic concepts of morphometry as well as demonstrates their application. A section is included which outlines some of the pitfalls encountered in non-random sampling of micrographs, artifacts due to shrinkage, section thickness, and specimen contrast. This article is designed to be a teaching tool which hopefully will stimulate botanists to apply these techniques in the future. DURING THE LAST FEW DECADES a significant amount of biochemical data on plant metabolism has been published. By their nature, these data are numerical and yield information on quantities of reactants and products as well as rates of reactions. In contrast to this, most cytological, ultrastructural, and cytochemical studies on plant cells have been largely qualitative. The quantification of cell structure using the techniques of morphometry yields results which can be related in a more meaningful way to biochemical data. For nearly 20 years (Elias, Henning and Schwartz, 1971; Weibel, Kistler and Scherle, 1966) zoologists have been applying stereological techniques of morphometric cytology to ultrastructural cytology. Such studies have yielded information on the absolute sizes and shapes of cells and organelles and on their rates of change in number, volume, and surface area during development. These studies have described the structural characteristics of cells and organelles and in conjunction with biochemical data, have established many of their associated functional roles in physiology (Loud, 1968). "Concepts" such as membrane efficiency can be determined knowing the pro1 Received for publication 7 July 1981; revision accepted 10 August 1981. The author wishes to thank Drs. Lida K. Barrett and Laszlo Hanzely for critically reviewing the manuscript; Drs. L. K. Barrett, Brenda Eisenberg, and Jerrold Zar for advice concerning various theoretical aspects of morphometry and statistics; Mark McLean and Deborah Toth for editorial assistance; Jane Glaser and Andrea White for technical assistance. duction of an organ, its volume, the number of cells within it, and the surface area of cell organelles. All of these quantities, except the first, can be obtained from random micrographs (both light and electron) using nothing more complicated than a clear sheet of lined acetate and a pocket calculator. For example, in Leydig cells of the rat, 1.0 gm2 of smooth endoplasmic reticulum and 0.3 gm2 of mitochondrial inner membrane on the average produce testosterone at a rate of one molecule/sec (Mori and Christensen, 1980). In general, botanical research has lagged far behind zoology in its application of morphometry to cytology. Few botanical papers have included morphometric techniques. The exceptions to this being some studies involving shoot apices (see Mauseth, 1980, 1981a, b, 1982a, b; Orr, 1981 for bibliographies) and cotyledon development (Briarty 1980a, b). This paper is an attempt to introduce botanists to stereological techniques of morphometric cytology. I will attempt to define the basic principles, and give examples of their application. These techniques can be applied to any structure which can be viewed in two dimensions (sectioned). HISTORY, DEFINITIONS, AND PRINCIPLESStereology is a new term coined in 1961 by the charter members of the International Society for Stereology (Elias et al., 1971). It is the threedimensional interpretation of two-dimensional (flat) images such as sections or projections. Stereology yields three-dimensional information from two-dimensional data, or two-di-