Claud L. Brown

Differentiation of Plantlets in Longleaf Pine (Pinus palustris Mill.) Tissue Cultured In vitro

Embryos of longleaf pine (Pinus palustris Mill.) were induced to form numerous adventitious buds along their cotyledons when placed in culture on chemically defined nutrient media. The buds when excised and transferred to other media form roots and vigorous plantlets. Plantlets were obtained from numerous embryos using three different seed sources. Histological observations describing these patterns of differentiation are presented.

The Effects of Flooding on the Swamp Forest in Lake Ocklawaha, Florida

A 26-km stretch of the Oklawaha River in north-central Florida was impounded in 1968, forming a 5265-ha reservoir and flooding 1620 ha of mixed deciduous hardwood swamp to depths up to 3 m. Carolina ash (Fraxinus caroliniana Mill.), baldcypress (Taxodium distichum (L.) Rich.), red maple (Acer rubrum (L.)), and swamp tupelo (Nyssa silvatica var. biflora (Walt.) Sarg.) were the important tree species, with smaller amounts of cabbage palm (Sabal palmetto (Walt.) Lodd), button bush (Cephalanthus occidentalis L.), and several species of oak and elm. Tree mortality 3 yr after flooding was closely related to water depth, but it also varied with species and diameter. All trees of all species had died in those parts of the reservoir flooded in excess of 1.3 m. Mortality decreased progressively as prevailing water depth decreased below 1 m. At 0.8 m mortality averaged 41%, at 0.7 m it averaged 17%, and at 0.2 m it averaged 2%, about the same as natural mortality in unflooded areas of the swamp. Baldcypress, swamp tupelo, and cabbage palm were the most flood tolerant. The oaks were least tolerant. Measurements at the end of the fourth, sixth, and seventh growing seasons showed that the rate of mortality had dropped to low but still above-natural levels. Under all flooding depths mortality was least in the larger trees, those >38 cm in diameter. Trees <13 cm in diameter suffered the greatest losses. As depth of water increased, the proportion of the root systems killed by flooding increased, and the amount of starch in tissues of living roots decreased.

Lenticel and Water Root Development of Swamp Tupelo Under Various Flooding Conditions

Seedlings of swamp tupelo (Nyssa sylvatica var. biflora [Walt.] Sarg.) were grown in nonflooded soil or soil that was intermittently flooded, continuously flooded, or surface-saturated with moving or stagnant water. Lenticels on nonflooded seedlings were round, only slightly hypertrophied, and had few closing layers. Degree of hypertrophy and number of closing layers per lenticel increased with surface saturation and intermittent flooding, but closing layers were absent under continuous flooding. Flooded lenticels remained nearly round despite variations in hypertrophy. In all treatments, intercellular spaces were abundant in the complementary tissue and phellogen because of the spherical shape of these cells. Although the continuity of intercellular spaces was interrupted because the closing layers anastomosed, breaks within the closing layers prevented these spaces from being completely blocked. Water roots developed primarily under continuous flooding in moving water, some apparently originating beneath the phellogen of a lenticel and others within the phellogen or its derivatives.

Permeability of the Cambium to Air in Trees Adapted to Wet Habitats

The permeability of the cambium to gas exchange varies significantly among tree species The amount of tension required to pull air across the cambium of water tupelo and green ash is sufficiently low to permit free gas exchange with the atmosphere, whereas air movement is restricted across the cambia of sweetgum, yellow poplar, and sycamore Water tupelo and green ash stems possess prominent intercellular spaces among the cambial ray initials forming an open interconnecting aeration system between the xylem and phloem rays on either side Similar openings in the cambium are absent or less than 1 μ in size in the other species examined. In mesophytic trees the transpiration stream undoubtedly plays a vital role in supplying oxygen to, and removing carbon dioxide from, the actively dividing and differentiating cells on the xylem side of the relatively impervious cambium Conversely, in hydrophytes where air is often limiting to the roots and water is plentiful the cambium is increasingly more permeable to air.

Cellular Differentiation of the Cambium in the Pinaceae

Patterns of cellular differentiation in the cambial zone of several members of the Pinaceae are discussed with attention focused upon the cambial ray initials. These initials consist of erect and radially elongate cells. The latter often extend across the zone of dividing axial elements and even into the mature xylem and phloem. The final form and maximum dimension of the radially elongate ray initials may be accurately determined only during mitosis, and asymmetric divisions are frequently observed because of a high degree of intracellular differentiation prior to division. Both fusiform and ray initials may be radially offset from their respective neighboring initials, and more specifically from each other, as a result of nonsynchronous mitotic activity and the extent of subsequent differentiation. Consequently, the concept of a uniseriate cambium does not require that all cambial initials be perfectly aligned radially to form a symmetrically cylindrical sheath surrounding the xylem. The continuity of the cambium is interrupted in some genera (Picea, Larix, and Pseudotsuga) by the radial continuity of open resin canals between the xylem and phloem.

Shoot Growth and Histogenesis of Liquidambar styraciflua L. Under Different Photoperiods

Sweetgum (Liquidambar styraciflua L.) seedlings were grown under three different photoperiods to determine the effect of daylength on the cellular composition of internodes. Cell counts and measurements were made of the pith and cortical cells in the mature internodes of the elongated shoots. Variation in final internode length as affected by position along individual shoots and by photoperiodic treatments was due to differences in number of cells and not to differences in cell lengths. Duration and rate of shoot growth significantly increased with increases in daylength, resulting in the production of more nodes and longer internodes. Total shoot height was more closely correlated with growth rate than with duration of growth, whereas the number of nodes produced was correlated more with length of the growth period.

Ultrastructure of paraquat-treated slash pine (Pinus elliottii engelm. )

The introduction of paraquat into the transpiration stream of young slash pine trees significantly enhances oleoresin biogenesis and results in localized resin soaking in treated portions of the bole. All affected cells of the xylem symplast, including those not directly assocated with resin ducts, begin to synthesize excessive oleoresin and secret or lose it initially through pits into the lumen of contiguous tracheids. Oleoresin is observed in plastids, mitochondrial envelopes, vacuoles, and ER cisternae in both control and treated trees. Cells near the site of paraquat treatment show extreme damage to membrane integrity, depletion of starch, and loss of cellular organization.

Suppressed Buds on Lateral Roots of Liquidambar styraciflua

Suppressed buds have been found imbedded in the periderm of lateral roots in sweetgum (Liquidambar styraciflua L.). These buds, when released from inhibition by natural or artificial means, may form typical short shoots or develop into normal long shoots during the season of release. The vascular traces of the suppressed buds may extend from the periderm to the primary xylem of the stele, which would indicate origin from primary tissues, or they may extend only through several growth rings to a point of earlier root injury. This is apparently the first observation of suppressed buds on roots of woody plants, but it is likely that they are present in other woody species that reproduce by root-suckers.