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28 December 2022 Production of growth centers in stems of three shrub species
Lance S. Evans
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Shrubs are dominant plants in many hot deserts with limited moisture throughout the world. Shrubs are woody plants of relatively low height, distinguished from trees by having several stems rather than a single trunk. Soon after seedling establishment, main stems of shrubs produce a large number of growth centers that produce independent stems. The purpose of this study is to describe the characteristics of growth centers in stems responsible for the production of independent stems in three desert shrub species. Samples were processed from the transition zone to about 30 mm above the transition zone. Axis splits and lobes were common in the three species. Growth centers were identified as areas of concentric circles of xylem cells. Concentric circles of xylem cells can only be produced by cambial cells. In some cases, axis splits directly fractured the vascular cambium to produce fragmented cambia to produce growth centers. In other tissues, axis splits were not visible but growth centers developed. Lobes may move cambial cells that may have temporarily ceased activity but may become active at a later date and begin producing cells to become growth centers. These cambial cells are from a fragmented cambium that have moved to various locations by axis splits and lobes. To our knowledge, this is the first study to describe the process of producing fragmented cambia in shrub species in tandem with axis splits and eccentric growth (lobes) of stems. Moreover, this is the first study to document the production of individual stems from individual fragmented cambia.

Lance S. Evans "Production of growth centers in stems of three shrub species," The Journal of the Torrey Botanical Society 150(2), 331-344, (28 December 2022).
Received: 21 August 2022; Published: 28 December 2022
axis splits in stems
Coleogyne ramosissima
eccentricity (lobes)
Encelia californica
fragmented cambium
growth centers
Sarcobatus vermiulatus
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