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Davis et al. introduce a new technique, the freezing centrifuge, to separate the interactive effects of xylem pressure and freezing on cavitation. The centrifuge method, modified to include freeze-thaw cycles, showed no freezing-induced cavitation under modest water stress in tracheid-bearing (small diameter) conifers vs. vessel-element (large diameter) bearing angiosperms, which showed nearly complete cavitation under the same conditions. Their results may explain why conifers thrive at high elevations and latitudes where freezing is common. (see p. 1367)

The core Malvales

Alverson et al. apply ndhF sequence data to long-standing phylogenetic questions concerning a group of families traditionally known as the core Malvales—Bombacaceae (baobabs, durians), Malvaceae (cotton, hibiscus), Sterculiaceae (cacao, cola nuts), and Tiliaceae (basswoods, jute). They present phylogenetic trees showing the 12 major clades and discuss homoplasy in morphological features common in this large group. Of the traditional families, only the Malvaceae comprise a natural group, and the malodorous durian and cacao each take new positions on the evolutionary tree. (see p. 1474)

Somaclonal variation in tissue-cultured spruce

Tremblay et al. present the results of a large study, ~11 000 plants in 87 clones of black and white spruce over 5 yr, of somaclonal variation in plants regenerated through somatic embryogenesis for future integration in reforestation programs. This tissue culture method can theoretically produce an unlimited number of genetically identical plants from a single seed, but phenotypic variation occurs at low frequencies, 1.0% for white spruce and 1.6$ for black spruce in this study. Tremblay et al. characterize this phenotypic variation into nine types and suggest reasons for the genetic instability. (see p. 1373)

Sapling architecture of rain forest trees

Poorter and Werger compared architecture and leaf display in saplings of six rain forest tree species in Bolivia. Their conclusions, that species show different ways to put biomass into their aboveground structures and that this is not related to differences in shade tolerance, are not new, but their focus in reaching these conclusions on a number of parameters, such as realized height and crown explansion as a function of unit support biomass, leaf position in the saplings, support mass, space to support mass ratio, and median leaf area, is new and gives an original insight into how a tree is structured. (see p. 1449)

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