SummaryCurrent theories of phosphorus uptake by plants imply that they can augment diffusion to their root axes by the development of abundant root hairs or mycorrhizas. Some phosphorus efficient plants have root morphology with multi-branched roots and localised regions of densely packed root hairs, which we suggest is better suited to the retention of substances exuded by the roots than uptake of substances moving to the root by diffusion. Evidence of substantial exudation by the proteoid roots of Lupinus albus is presented.

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Large quantities of citrate ions have been shown to be secreted by the roots of Lupinus albus. It is postulated that these react in the soil to form ferric hydroxy phosphate polymers which diffuse to the root surface where they are degraded by the action of reducing agents in the presence of an Fe II uptake mechanism balanced by hydrogen ion secretion. Some known chemical behaviour of Fe III and citrate which supports this postulate is reviewed. Evidence is also presented which suggests that much of the Fe absorbed circulates within the root system and is subsequently precipitated.

This monograph describes the genus Phyllachora as it occurs on members of the Gramineae, discusses the reliability of criteria for delimiting species, and gives a taxonomic account of the Phyllachora species found on grasses. A world-wide survey of graminicolous Phyllachora specimens has led to the conclusion that of the 278 species and varieties named in the literature, only 95 are valid species and a further 21 are doubtful species. Of the 95 valid species, three (P. americana, P, longinaviculata, and P. microsperma) have been given new names, and five (P. bulbosa, P. koondrookensis, P. platyelliptica, P. polytocae, and P. rostellispora) are new species. Two species complexes are discussed. The P. fallax complex includes four species which, although fairly readily separated, have several features in common and may be better delimited in future as varieties. The P. shiraiana complex includes seven bambusicolous species, few of which have been seen by the author, and the published descriptions of which are closely similar. It is possible that six of these species are synonyms of P. shiraiana s. str. A key to graminicolous Phyllachora species and a guide to its uses are provided as well as a host index, including 135 grass genera, and an index to Phyllachora species, their synonyms, and doubtful species.

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