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  • Author or Editor: H. M. Pellett x
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Abstract

Deep supercooling of stem tissue water was found in all the native species of rose (Rosa spp.) studied. Freezing of this supercooled water was associated with injury to the stems, indicating that maximum cold hardiness of these species is limited to about −40°C. Therefore, these species have some potential for use in breeding to develop cold-hardy cultivated roses, but their hardiness would be limited to −40°C by the supercooling characteristic.

Open Access

Abstract

Roots of ‘Mailing (M) 26’ and ‘Malus robusta (MR) 5’ were less hardy than stems in winter; hardened more slowly in fall; and dehardened later in spring. In 1967 roots were hardier than in 1968, despite slightly higher soil temperatures. This difference in hardiness was associated with much less rainfall in 1967 leading to a lower level of root hydration. While overall soil temperature-hardiness relationships were unclear, short-term changes in root hardiness were correlated with soil temperature during the preceding week. Hardening in apple roots appeared to be influenced by soil temperature and level of root hydration.

Open Access

Abstract

Stems of 49 woody species native to North America were collected from the field in Minnesota in January and subjected to controlled freezing tests. Characterization of the freezing process of xylem tissues by differential thermal analysis revealed that some species had no exotherms at low temperatures, some had small exotherms between –41° and –47°C, and others had large exotherms in the same temperature range. Generally very hardy species with ranges extending into northern Canada and Alaska had no exotherms. Species with small exotherms were native to the northern United States and southern Canada, and large exotherms were generally characteristic of the least hardy species studied. The low temperature exotherms occurred at the same temperature that results in xylem death of most of the plants studied. Plants with low temperature exotherms tend to have ring-porous xylem and the temperature of the low temperature exotherms was correlated with the minimum temperatures of the boundaries of the northern range of the species tested.

Open Access