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Polyethylene glycol (400) with 90% glycerol (aqueous) is introduced as an efficient solvent system for lipid stains. Various lipid-soluble dyes were dissolved in this solvent system and tested for their intensity, contrast, and specificity of staining of suberin lamellae in plant tissue. The stability (i.e., lack of precipitation) of the various staining solutions in the presence of fresh tissue was also tested. When dissolved in polyethylene glycol-glycerol, Sudan red 7B (fat red) was the best nonfluorescent stain and fluorol yellow 088 (solvent green 4) was an excellent fluorochrome. These two dyes formed stable staining solutions which efficiently stained lipids in fresh sections without forming precipitates. Estimations of the solubilities of these dyes in the solvent compared with their solubilities in lipids of various chemical types indicated that they should both be effective stains for lipids in general.

The phenology, root anatomy, and mycorrhizal colonization of vascular plant species occurring in a hardwood forest site were studied. Sugar maple (Acer saccharum), the dominant tree, ash (Fraxinus americana), another important tree, and the most abundant herbaceous plants were examined periodically. Most of the herbaceous species present were highly colonized by vesicular–arbuscular mycorrhizae (VAM), but some consistently had low levels of VAM, or were nonmycorrhizal, and several had orchid mycorrhizae. Most trees were associated with VAM, although several ectomycorrhizal species occurred in low numbers. Herbaceous plants could be divided into four phenological categories of shoot activity, spring, spring–summer, summer, and fall, but many species had periods of root growth that did not parallel their aboveground activity. Almost all species that produced new roots in summer were well colonized by VAM, while those active mainly in late fall or early spring tended to be nonmycorrhizal. Roots of the woodland plants typically had a well-developed exodermis and also tended to be long-lived and coarse. Possible relationships among these root system characteristics, phenological categories, and levels of mycorrhizal colonization of woodland plants are discussed.

BRUNDRETT, M., MURASE, G., and KENDRICK, B. 1990. Comparative anatomy of roots and mycorrhizae of common Ontario trees. Can. J. Bot. 68: 551-578.The structure of roots and mycorrhizae of trees belonging to 20 important Ontario tree genera were examined. During this study efficient methods for examining root anatomy were developed, and tree root information was compiled. The ultimate lateral roots of most species examined were consistently mycorrhizal, and many species had heterorhizic root systems with separate long and short lateral roots. Tree roots displayed enough structural diversity in features such as thickened, lignified, or suberized walls, and secondary metabolite-containing cells to allow identification of genera. The roots of trees belonged to four major anatomical groups as a result of the major differences between angiosperm and gymnosperm roots, and between those with ectomycorrhizal (ECM) or vesicular-arbuscular mycorrhizal (VAM) associations. (i) Members of the Pinaceae had structurally similar heterorhizic roots that had ECM with a cortical Hartig net. (ii) Thuja (Cupressaceae) had distinctive nonheterorhizic roots with phi thickenings and VAM. (iii) Angiosperms with ECM belonged to diverse families, but all had similar heterorhizic root systems with ECM short roots that had an epidermal Hartig net and a narrow cortex of thick-walled cells. (iv) Most angiosperms with VAM had nonheterorhizic roots, and this group had the greatest diversity of root structural features. Possible structural and defensive roles of root features and potential influences of these features on mycorrhizal formation are considered.BRUNDRETT, M., MURASE, G., et KENDRICK, B. 1990. Comparative anatomy of roots and mycorrhizae of common Ontario trees. Can. J. Bot. 68 : 551-578. Les auteurs ont examink les structures des racines et des mycorhizes d'arbres appartenant a 20 genres d'arbres importants en Ontario. A I'occasion de cette Ctude, des mCthodes efficaces pour Ctudier l'anatomie racinaire ainsi que des informations sur les racines des arbres ont CtC dkfinies. Les racines laterales ultimes de la plupart des espices examinCes Ctaient normalement mycorhizCes et plusieurs espices montrent des systkmes racinaires hCtCrorhiziques oh on retrouve des racines longues et des racines 1atCrales courtes. Les racines montrent suffisamment de diversit6 structurale dans leurs caractCristiques telles que les parois cellulaires Cpaissies lignifiCes ou subCrifiCes et dans le contenu cellulaire en mktabolites secondaires pour permettre l'identification, du moins au niveau des genres. Les racines des arbres appartiennent 2 quatre groupes anatomiques majeurs; ainsi, les differences principales se retrouvent entre les racines des angiospermes et des gymnospermes aussi bien qu'entre les racines ectomycorhizCes (ECM) et endomycorhizienne a vCsicule et arbuscule (VAM). (i) Les membres des Pinaceae ont des racines hCtCrorhiziques de structure similaire, avec ECM et rCseau de Hartig cortical. (ii) Le genre Thuja (Cupressaceae) montre des racines ty...

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Many detritus-feeders prefer dead leaves which are colonized by microorganisms-i.e. conditioned leaves, over freshly fallen or sterile leaves. Traditionally, this has been attributed to the build-up of microbial cells on the substrate. Two experiments show that changes in the leaf itself, brought about by microbial excretions and secretions, or by a hydrolytic agent (hot HCl), can also increase its palatability to the detritus-feeding amphipod Gammarus pseudolimnaeus.

SUMMARYThe morphology of vesicular-arbuscular (VA) mycorrhizas in the roots of five species of herbaceous woodland plants, in which root growth and mycorrhiza formation were quantified in the first part of this study was examined, i he root anatomy of these species was also examined in detail, using various staining procedures to observe cell wall structure, especially in the region where mycorrhizal colonization was initiated. The morphology of mycorrhizal colonies within the roots of these species was observed at different stages of development using light microscopy. It was found that modifications of endodermal and exodermal cell-walls could determine the way in which fungi entered the roots. It was also found that properties of the cortex considerably infiuenced the localization of hyphae and arbuscules within roots. Features of VA mycorrhizas that were probably associated with particular endophytes were also noted. It is considered likely that some aspects of root structure have evolved means of regulating the efficiency of mycorrhizal associations.

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