The pollination mechanism of Picea engelmannii (Parry) was studied on small potted scions under natural conditions and in controlled environment chambers. Six stages of conelet development were recognized and related to pollen receptivity. Cone-lets appeared receptive for about 2 weeks but were actually receptive for only about 1 week. Secretory droplets appearing on the micropylar arms collected pollen for several days before pollination drops formed. Pollination drops formed acropetally in the conelet and only once from each ovule. Pollination caused rapid recession of the pollination drop, whereas the drop remained for several days on unpollinated ovules. There was some decrease in size of pollination drops during midday and reemergence the following night. Pollination drops were secreted by the nucellar tip in a manner similar to nectaries. Secretory cells collapsed following secretion. The drop contained 4.3% glucose and 3.8% fructose but no sucrose. High humidity increased the longevity and decreased the diurnal fluctuation in size of pollination drops. Conelets from trees with low leaf water potential developed more slowly and produced smaller and more viscous pollination drops. Cones averaged 103 ovuliferous scales, 90% of which were fertile. However, usually less than 50% of the potential seed set was achieved. One of the major causes for low seed set is inadequate pollination. A better understanding of the pollination mechanism and the receptive period may improve seed efficiency in controlled and supplemental mass pollinations.

Production of seed cones from 1978 to 1987 and of pollen cones from 1980 to 1982 by young black spruce (Piceamariana (Mill.) B.S.P.) trees was recorded in five plantations aged 8, 10, 12, 14, and 16 years in 1980. Variations in cone production and percentages of trees bearing cones were assessed in relation to changing tree age and cone numbers per tree. The first seed cones and pollen cones were noted on 7- and 10-year-old trees, respectively. After ages 10–12 for seed cones and 12–14 for pollen cones there were substantial yearly fluctuations of average numbers of cones per tree. Similarly, the percentages of trees bearing cones fluctuated among years, but differences between poorer and better years decreased as the proportion of bearing trees gradually increased. Up to age 14, the number of seed cones borne per tree was generally higher than the number of pollen cones. Thereafter, pollen-cone production was always higher than seed-cone production and reached 6.6 pollen cones per seed cone by age 18. Pollen cone bearing trees were good indicators of seed cone bearing trees at all ages. Most 12-year-old and older seed cone bearing trees were good indicators of pollen cone bearing trees. Annual production of seed cones was correlated with warm weather in early May and early July, and with relatively low rainfall in early June of the previous year.

The distribution of seed cones on shoots, on branches, and within the crown was determined for young Piceamariana (Mill.) B.S.P. (black spruce) trees aged 6–18 years. The seed-cone zone was restricted to distal 1-year-old shoots until ages 7 and 8. It expanded with increasing tree age, and in association with increases in cone numbers, to include older branches and a great variety of smaller shoots on those branches. By age 18, about 25, 55, and 20% of the cone crop was borne by 1-, 2-, and 3-year-old branches, respectively; hence, a concentration of cones, typical of the species, was maintained near the tree apex. Order 1 shoots bore all cones up to tree ages 7 and 8, but proportions on such shoots decreased with increasing tree age. By tree age 18, order 1, 2, and 3 shoots bore 27, 72, and 1% of the crop, respectively. Seed cones occurred progressively from proximal to distal and finally terminal positions on shoots of different categories following three patterns of decreasing shoot vigour (length). Medial and distal cones were most common. Terminal cones were located only on the weakest shoots within the seed-cone zone.

No abstract

Black spruce (Piceamariana (Mill.) B.S.P.) cones were collected in 1980, l981, and 1982 from young trees in four plantations of different ages. Nine measures of cone size, seed yield per cone, and seed weight were determined by cone analysis, and the variation among plantations and years was assessed by analysis of variance. Relationships among the nine measures were assessed by correlation. Cone length, cone weight, total scales per cone, potential filled seeds per cone, total seeds per cone, total filled seeds per cone, and seed efficiency were all depressed in 1981, the year of poorest cone production. Potential filled-seed yield and actual filled-seed yield were highly correlated with most cone-size measures but poorly correlated with each other. Pollen availability in 1982 was assessed by trapping and by counting pollen cones. The catch of pollen grains was positively correlated with the numbers of pollen cones per tree. Total filled seeds per cone in 1982 was strongly related to pollen availability. Seed efficiencies of less than 35%, which occurred in the younger plantations and in the year of poorest pollen-cone and seed-cone production (1981), indicated excessive loss of potential seed.