OWSTON, P. W. 1969. The shoot apex in eastern white pine: its structure, seasonal development, and variation within the crown. Can. J. Bot. 47: 1181-1 188. Structure of the shoot apex in eastern white pine (Pin~rs strobus L.) was similar to that described for other members of the genus. The overwintering bud contained all primordia for the next season's growth, and the apical meristem exhibited ginkgoid cytological zonation. Seasonal development at the shoot apex was divided into three phases: dormancy, extension of overwintering bud accompanied by formation of new cataphylls, and formation of primordia in the axils of some cataphylls. Terminal shoot apices decreased in size and number of primordia with lower position in the crown. Heightldiameter ratio of the apical meristem increased with lower crown position, and cytological zonation was absent in apices in the lowest part of the live crown. Such variation within individual trees makes it difficult to describe or compare species on the basis of limited sampling. By late summer or early fall of the present study, dwarf shoot primordia possessed sheath scale and needle primordia. But primordia of flower buds and lateral vegetative buds could not be distinguished from them. Past work with soft pines has shown similar results. Hard pines, on the other hand, have been shown to differentiate flower bud primordia during the season of their formation.

Seedlings of Pseudotsugamenziesii (Mirb.) Franco, Abiesprocera Rehd., and Piceasitchensis (Bong.) Carr. were grown for 5 months in growth rooms which simulated hot, warm, or cool growing regimes in greenhouses in western Oregon. Temperature, humidity, light intensity, and photoperiod were changed diurnally and seasonally. In all three species, maximum heights of seedlings were attained in the hot regime, whereas stem diameters were similar under the hot and warm regimes. Dry weight increment was greatest in the warm regime. The cool regime was suboptimal for all aspects of growth. Seedlings grown in the hot regime were least resistant to cold in early fall. Differences in resistance to cold of seedlings grown in the warm and cool regimes varied by species and type of damage.

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Field performance and root form of container-grown Pinnsponderosa Laws. seedlings were studied after application of three treatments and compared with untreated bare-root seedlings. One-year-old seedlings grown in 1.9-ℓ milk carton containers were treated by (1) removing the bottom of the container, (2) removing the whole container, and (3) removing the whole container and cutting spiralled roots off at the bottom of the surface of the root ball. Survival was excellent for trees of all treatments. Bare-root seedlings grew most in height the first season, but after 5 years, the average height of container seedlings was greater than for bare-root trees. Seedlings with container removed and roots cut were tallest and had root systems that appeared sturdiest. Most of these had well developed taproots and good outward growth of laterals with little spiralling. Aborted or kinked taproots and spiralled laterals were often found where only the bottom of the container had been removed.