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Two papers in this issue, one by Sperry and Hacke and the other by Hacke, Sperry, and Pittermann, significantly advance our understanding of the structure and function of pits in the xylem walls of angiosperms and gymnosperms. The authors model the hydraulic and mechanical properties of the pits with thoroughness and skill, building up a most impressive understanding of the processes by which they fail. The idea of the cost of resistance to cavitation in the form of higher resistance and the need for thicker xylem walls is well developed and sheds new light on the functional trade-offs in the design of xylem. (see p. 369 and p. 386)

Phylogeny of lichen-forming fungi

Miadlikowska and Lutzoni propose a new classification for peltigeralean lichen-forming fungi (see front cover). These fungi form bipartite symbiotic associations with cyanobacteria and tripartite associations when a green alga joins the symbiosis. Maximum likelihood reconstruction reveals bipartite associations with cyanobacteria as the ancestral symbiotic state within these fungi. (see p. 449)

Cytokinesis in Coleochaete

Using differential interference contrast optics, Cook recorded images, in different focal planes over time, of cytokinesis in living cells of Coleochaete orbicularis to determine whether a newly described kind of cytokinesis (Cutler and Ehrhardt, 2002, Proceedings of the National Academy of Sciences, USA 99: 2812-2817) might occur in this close relative of land plants. It did. This significant contribution clarifies misinterpretations in the literature as well as opens the way for further comparisons between key land plant and green algal taxa. (see p. 313)

The four-celled gametophyte

The female gametophyte development of Illicium, one of the basalmost angiosperms, is the subject of a comprehensive, well-illustrated study by Williams and Friedman. The authors clearly show that the embryo sac is four-nucleate and not eight-nucleate as in most other angiosperms. This condition is associated with lack of nuclear migration to opposite poles in the two-nucleate stage. In their paper the authors consider features that have been neglected in other embryological studies but which turn out to be of great interest for understanding embryo sac development. (see p. 332)

This Article Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Search for Related Content