Major eastern shade-intolerant/intermediate coniferous species

Larix laricina (Du Roi) K. Koch. - tamarack (tamarack larch or eastern larch)

Image 1. Distal portion or overwintering long shoot (or twig) showing a terminal bud and several lateral buds in axils of some of the leaf scars.

Image 2. Scanning-electron micrographs (each at the same magnification) of overwintering buds from which the surrounding bud scales have been removed, all equivalent views looking down on the tops of the exposed bud content: upper left, a terminal bud showing the shoot apex (A) with axial-leaf primordia (AL) on a conical shoot-primordial axis produced earlier from, and below the shoot apex, and a ring of large basal-leaf primordia (BL) arching over the outer flanks of the shoot-primordial axis; upper right, a lateral bud from the distal region of the same long shoot from which the terminal bud was taken, its parts and structure is similar, but numbers and sizes of strctures are smaller; lower left, a large lateral bud from the mid-region of a long shoot, showing a large quantity of basal-leaf primordia, the shoot apex is hidden in the depths at the centre and there are no axial-leaf primordia (this is unusual form of short-shoot bud); lower right, a small lateral bud from the proximal region of the same long shoot from which the terminal bud was taken, showing a substantial number of basal-leaf primordia, the shoot apex being hidden - the two upper buds are typical long-shoot buds, the lower right bud is a typical short-shoot bud, the lower left bud is an unusual form of short-shoot bud, somewhat intermediate between a long-shoot and a short-shoot bud (from Remphrey and Powell 1984, Can. J. Bot. 62: 2181-2192).

Image 3. Distal portion of the previous year's leader on which long-shoot buds have burst, the basal leaves of the new long shoots have extended, and the axial portions of the new long shoots are visible within the clusters of basal leaves; the new shoot at the bottom left is a new short shoot with "basal" leaves only, early June.

Image 4. Previous year's long shoot of a lateral branch on which a new long shoot is developing terminally (and showing a negatively geotropic response as the extending, new axial portion is oriented upwards at its distal end), and two distal lateral long shoots are developing; the rest of the new shoots are short shoots with clustered "basal" leaves, early June.

Image 5. A new lateral long shoot in early stage of development as the axial portion reaches the length of some of the surrounding basal leaves, late May.

Image 6. The axial portion of an extending long shoot, the spreading basal leaves around its base have sharply incurved tips; neoformed axial-leaf production and shoot elongation is under way, mid-June.

Image 7. New shoot expansion along the previous year's leader: the new leader (a long shoot) and the new (distally situated) lateral long shoots are vigorously elongating with probably all their preformed axial leaves now extended, and neoformed axial-leaf production and extension occurring, their preformed basal leaves form large clusters around the shoot bases: below these long shoots, and along the proximal portion of the previous year's leader are short shoots with their clusters of "basal" leaves fully expanded, and their apical meristems now producing bud scales for their new terminal buds, late June.

Image 8. The upper two years of development of a vigorously growing sapling just after bud burst, early May: this tree lacks syllepsis on the leaders of the two previous years (compare image 9).

Image 9. The upper two years of development of a vigorously growing sapling just after bud burst, early May: this tree has copious sylleptic branching on the leaders of the two previous years (compare No. 8, both trees were growing in close proximity in the same 5-year-old plantation), note that in each of the previous years the sylleptic branches occurred in the upper portion of the lower half of the respective leader.

Image 10. Sylleptic branches (sylleptic long shoots) developing along an elongating leader, mid-July

Image 11. An elongating sylleptic long shoot developing in the axil of a leaf of an elongating leader: other similar leaves lack axillary structures or have well-developed axillary (lateral) buds, as does the one partially shown at the base of the picture, mid-July.

Image 12. Sylleptic short shoots (see Remphrey and Powell 1985, Can. J. Bot. 63: 1296-1302) developed along an elongating leader, mid-July: the sylleptic short shoots shown have four or five visible leaves and little shoot extension, one shows its developing terminal bud; each sylleptic short shoot developed in the axil of a leaf on the leader but as development proceeded leader elongation carried the shoot some distance away from the subtending leaf (this frequently occurs with different kinds of lateral or "axillary" structures, see Powell 1987, Can. J. For. Res. 17: 490-498).

Image 13. An overwintering sylleptic short shoot showing pulvini or elongated leaf cushions of six leaves with their leaf-scar positions and a fully developed terminal bud: the leaf scar and the tip of the elongated leaf cushion of the subtending leaf is at the right.

Image 14. The base of an overwintering sylleptic long shoot showing its clear origin from the parent long shoot (a tree leader) without an intervening ring of bud scales or bud-scale scars: the leaf scar of the subtending leaf is evident, as also is a lateral bud and its subtending leaf scar on the surface of the leader.

Image 15. An overwintering portion of a two-year-old tree leader with, at the left, the base of a two-year-old sylleptic long shoot (without a ring of bud scales around it), and, at the right, the base of a one-year-old proleptic long shoot that has clearly arisen from a lateral bud, the ring of bud scales of which is evident, as also is an inner ring of basal-leaf scars: the one-year-old proleptic long shoot bears a lateral bud in the axil of one of its axial-leaf scars; in contrast, the two-year-old sylleptic long shoot bears a one-year-old proleptic short shoot complete with its ring of bud scales, an inner ring of "basal"-leaf scars, and a fully formed terminal bud.

Image 16. The proximal portion of an overwintering one-year-old long shoot bearing a proximally situated lateral pollen-cone bud on its under surface and a more distally situated lateral short-shoot bud.

Image 17. A portion of an overwintering two-year-old long shoot bearing on its under surface, a one-year-old proleptic short shoot with a terminal pollen-cone bud, and on its upper surface, a one-year-old proleptic short shoot with a terminal short-shoot bud: each of the one-year-old proleptic short shoots has a ring of bud scales around its base and an inner ring of "basal"-leaf scars (clearly visible on the one on the upper surface).

Image 18. A portion of an overwintered two-year-old long shoot bearing one-year-old proleptic short shoots, from the terminal bud of the lower one of which, a pollen cone has emerged, and from the terminal bud of the upper one, the leaves of a short shoot can just be seen: the individual microsporophylls and microsporangia (pollen sacs) of the pollen cone can be seen, mid-April.

Image 19. A pollen cone shortly before pollen is shed: the pollen sacs are pink and the tips of the microsporangia are green, late April.

Image 20. A shrivelling pollen cone after having shed its pollen, mid-May.

Image 21. The proximal portion of an overwintering one-year-old long shoot bearing a proximally situated lateral seed-cone bud on its under surface and three lateral short-shoot buds.

Image 22. A portion of an overwintering two-year-old long shoot bearing on its under surface a one-year-old proleptic short shoot with a terminal seed-cone bud, and, more distally, two one-year-old short shoots each with a terminal short-shoot bud: each of the one-year-old proleptic short shoots has a ring of bud scales around its base and an inner ring of "basal"-leaf scars (clearly visible on the most distal one).

Image 23. A lateral seed cone (right) at the early receptive stage, late April or early May, and a short shoot emerging from its bud (left): the seed cone has clustered "basal" leaves below it, the pink structures are bracts which extend to serve as the "pollen catching or directing structures", note that each bract has (in this case a greenish) extended central point or awn.

Image 24. A receptive seed cone terminating a one-year-old short shoot, late April: note the vertical orientation of the cone, the ring of old bud scales around the short shoot, and the ring of new bud scales; between these rings of bud scales is a ring of leaf scars from the leaves of the previous year's short shoot.

Image 25. A receptive yellow-green lateral seed cone (right) and new lateral (proleptic) short shoots with their leaves elongating, late April or early May.

Image 26. Several dark pink seed cones, just past the receptive stage (the bracts have changed their orientation from somewhat horizontal to erect, and have thus closed against one another and sealed the cone), and many short shoots with rapidly elongating leaves forming typical clusters: the cones and the short shoots are all terminal on one-year-old short shoots, early to mid-May.

Image 27. A pink seed cone situated terminally on a short shoot, with its basal leaves extended: the more or less erect bracts have been pushed somewhat apart by the now vigorous upward growth of the ovuliferous scales (the cone scales) between them (each bract bears a cone scale in its axil), late May.

Image 28. A yellow seed cone situated terminally on a short shoot, with its basal leaves extended: round-edged, not awned, cone scales have grown up between the awned bracts such that, except at the base, only the tips of the bract awns remain visible, early June.

Image 29. A pink seed cone, close to final size, with all bracts overgrown by cone scales, early July.

Image 30. A yellow seed cone, close to final size, early July.

Image 31. Full-sized seed cones with cone scales beginning to turn pale brown, mid-July: note the new long shoot at the left.

Image 32. A mature "open" seed cone (in November) developed terminally on a one-year-old short shoot, and from which seeds have mostly been shed (whipped out from between the slightly spread-out scales by the wind): the bud scales from its own bud have now turned essentially black, beyond them and below the cone itself is a short section of shoot that bore the basal leaves around the cone ergone more elongation than a typical short shoot, but less than a typical long-shoot section; it forms the "stalk" that is characteristic at the base of a fallen seed cone.

Image 33. Winged seeds of Larix laricina: some show the under surface of the seed that was attached, during development, to the underlying cohe underlying cone scale; others show how the wing base covers the upper surface of the seed, on the under surface, a portion of the extreme base of the wing is seen to extend over the base of the seed (the scale bar across the bottom of the picture is in millimetres).

Image 34. A pink seed cone from the apex of which a long shoot is developing by neoformed growth (mid-June): such "proliferating seed cones" are fairly common in Larix laricina; such a shoot, although it produces lateral and terminal buds, generally dies, because the cone that carries it dies as it matures during August.

Image 35. A section of the upper crown of a sapling showing the leader of the previous year and many proleptic (one-season-old) long shoots in late October when yellowing and then abscission of leaves occurs: note how all the basal leaves have been shed, and how change in colour and then abscission of axial leaves is occurring acropetally, that is progressively from the base towards the tip of the long shoots, some of the most distal (the last-formed neoformed leaves) are still essentially green (see Powell 1988, Trees 2: 150-164).

Information provided by:
Dr. G.R. Powell
Faculty of Forestry and Environmental Management at UNB