substances have dominated more than a century of research into the flow of solutes in the phloem. One is that the movement takes place by a process analogous to diffusion; the other is that there is a mass movement in a stream through the sieve tubes of the phloem system. Based on the authors' work and on the entire body of literature concerning the movement of solutes in the phloem, this monograph offers the most complete analysis of phloem transport available in one source. Citing some 700 contributions to the literature, most of them made within the past decade, the authors arrive at some new conclusions about the physical and chemical factors associated with the transport of solutes in phloem tissue. Proceeding further, they lay a foundation for the eventual explanation of the mechanism that facilitates movement in all plant tissues. Every factor related directly or indirectly to phloem transport is discussed, documented, and interpreted. Many previously ambiguous concepts are clarified, and areas that require further research are noted. The first part of Phloem Transport in Plants provides a detailed analysis of the structure of phloem, the mechanism of phloem transport, and the phenomenon of phloem plugging. The authors discuss experimental work employing electron microscopy, tracers, and the collection of phloem exudate from aphids and aphid mouthparts; they also examine evidence of the flow of assimilates, hormones, and exogenous substances for information that confirms, or alters, contemporary beliefs about transport within the phloem system. Ways in which environmental factors influence translocation are discussed, as are some of the complex quantitative aspects of assimilate distribution.

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