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Mycotrophy Forest tree mycorrhizae receive continued attention from two of the principal investigators of mycotrophy. Rayner (1941) has summarized her own and related researches on the effect of composts on tree growth. Melin's (1946) attention has been turned especially to growth and anti-bacterial substances with respect to mycotrophy. Recently fallen leaf-litter was found to contain water-soluble substances that promoted the growth of litter-decomposing and mycorrhizal fungi. Cognate studies have been made by Harley but his latest paper was not available at this writing. Early Studies on Root Hairs:-Early observers were perhaps influenced by knowledge of circulation of blood in animal bodies and were doubtless expecting to find vessels in plants. When Malpighi found root-hairs on elm, black poplar, and willow roots, he assumed that these structures took up crude sap and passed it on to vessels. Grew, publishing about the same time (1682) had decided that spongy ends of roots served admirably for absorption of water and food from the soil; and Hales in 1727 and de la Baisse in 1733 tried to show experimentally that the greater quantity of water used by the plant was taken up through ends of the root-tips and that root-hairs were only incidental phenomena. To these hypotheses was added in 1768 that of S. Simon, who stated that roots, at least the noduliferous, are merely excretionary organs which serve to eliminate excess elaborated sap from the plant. In the earliest years of the nineteenth century, Garradori showed that root-hairs are wanting in water, from which fact he concluded that root hairs serve for absorption of moisture from the air and not for absorption of liquid water, which, he concluded, must be taken up by the spongy ends of roots. But, according to Moldenhawer, root-hairs may be compared to druse-hairs of leaves : they secrete a liquid which serves Kelley-2-Mycotrophy to dissolve food materials somewhat as saliva does in animals. It was F. Meyen, in 1838, who came to the modern view that root-hairs serve merely to increase the outer surface area of the root. By such studies attention was focused on root-hairs until Botany was firmly moulded to the view that higher plants are nourished by a root-hair mechanism. So positive had Botany become that by 1883, Frank Schwarz (from whom we have quoted much of the preceding paragraph) was able to state without exciting contradiction: "From my researches it may be stated that root-hairs are present on most plants, and when a plant fails to produce root-hairs it may be counted an exception." He listed as exceptions : water and swamp plants, and those the water and salt requirements of which are met in a special way, as in conifers, noduHferous plants and in part by parasites. Early Study of Nodules:-Thus it was, not by extended observation or study of plants in nature but by sheer dogmatism that root-hairs came to be regarded as the predominate root structures of higher plants. Hairless roots were considered exceptional, but they were constantly being note...

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