Forty-two Eurasian Scots pine (Pinussylvestris L.) clones in a Nebraska seed orchard were observed over 3 years for the phenology of pollen release and seed-cone receptivity and for the production of cones and filled seed. A preliminary investigation had indicated that seed yields were less than expected, and nonsynchronous flowering phenology due to wide genetic diversity was considered as a possible cause. The clones were divided into six regions based on geographic origin and analyzed for variation between regions and between clones within regions. Most variation in cones per tree and filled seeds per cone was due to differences between clones. Most variation in weight per seed was due to differences between regions. The order in which clones began releasing pollen and became receptive remained the same from year to year, but the duration of these events differed between years. Results indicated that nonsynchronous flowering phenology due to genetic diversity is not a likely cause of low seed yield. Seed crops (19.3 kg/ha, 97 000 seeds/kg) were not necessarily lower than should be expected, but 90% of a given year's crop was produced by an average of only 26 clones. With the paternal contribution of each clone to the seed crop unknown, collecting and sowing seed separately by clone is recommended.
Seasonal changes in the development of reproductive structures are documented for Populus trichocarpa Torr. and Gray. Buds were collected and studied from several trees for a 2‐yr period, but to maintain a congruous phenology, representative structures from only one male and one female tree are presented. Collected tissues were fixed, dehydrated, embedded in wax, sectioned, and differentially stained. The development of reproductive meristems begins early in the spring, before leaves emerge. However, the anatomy of male and female flowers is virtually indistinguishable until late spring. The structures of the gynoecium develop in about 2 wk, then continue to enlarge through the summer and autumn until the trees become dormant. The unilocular ovary consists of usually three, but sometimes four carples. Stamen development begins in the center of a disk‐shaped meristematic region and proceeds centrifugally. Megasporogenesis and microsporogenesis take place late in the winter, approximately 2 wk before anthesis. Dissection of mature flowers revealed 30–50 seeds per capsule on female trees and 40–60 stamens on male trees. When compared to most other Populus species, P. trichocarpa has a relatively large number of reproductive structures.
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