Thursday 12 December 2019

Distinctive black buds of the Ash visible at this time of year

Ash trees have big black buds at this time of year
Ash trees have big black buds at this time of year

Jim Hurley - Nature Trail

Ash, a member of the Olive family, is a very common tree and though it stands bare of leaves at this time of year it is immediately recognisable by its jet black winter buds. Unlike the sticky and shiny buds of the Horse-chestnut, the fat, pointed buds of the Ash are dry and matt.

The bud at the end of each twig, the terminal bud, is the biggest and fattest of the buds. When it opens in spring, it gives rise to new twig rather than a leaf. As the bud opens its scales fold back and break off allowing the new growth to emerge and the twig to extend in length.

In the image above, this year's large terminal bud is at the top right and at the bottom left the scars of the broken off scales of last year's terminal bud can be seen girding the twig and forming a distinctive girdle scar.

It follows that the distance between this year's large terminal bud at the top right and last year's girdle scar at the bottom left is the amount the twig grew during the past year.

One can search back along the twig for previous girdle scars, but they are difficult to impossible to see as they become obscured by the growth in girth of the twig.

But, back to the big terminal bud that gives rise to new twig. Note that it is flanked by two smaller buds. These are leaf buds and they tell us that the leaves in Ash are opposite: they grow in pairs, one opposite the other.

Note too that the next pair of leaf buds down the twig are at right angles to the pair above and below. So, not only are the leaves opposite, they are alternate: they alternate from one pair growing left and right to the next pair growing front and back and so on. It's an adaptation to get maximum light.

The shield-shaped scar of last year's leaf can be seen under this year's leaf bud. The angle between any leaf and its twig is called the axil so this year's bud is axillary: it is growing in the axil of last year's leaf.

Finally, lenticels are visible along the twig, These are tiny, raised, cork-lined bumps and are the breathing pores through which the inner living tissues of the twig exchange gases.

All of these features are worth examining out-of-doors on your local Ash tree.

Wexford People

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