2 posts in the category

Dendrology

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treeblog Set D: pretreatment of the rowan seed

So I’ve (1) collected and (2) pre-pretreated treeblog’s Set D rowan seeds. Now they are undergoing (3) pretreatment before I (4) plant them in the spring. The last time I planted rowan seeds – for treeblog Set C – I neglected to pretreat them and my folly was rewarded by a total absence of germination. (So far… A year of ‘natural pretreatment’ and they may yet germinate alongside the Set D seeds!) This time I am boosting my chances of success by trying out three different methods of pretreatment advised by the Forestry Commission in their Practice Guide Growing trees and shrubs from seed by Peter Gosling (2007) [available online in .pdf format here].

Rowan seeds are classed as orthodox, deeply dormant seeds – ‘orthodox’ meaning easily stored and ‘deeply dormant’ meaning they ‘remain outwardly inactive under all conditions’, i.e. they require pretreatment to bring about germination. In the wild, rowan seeds would remain dormant for a year or two before germinating – the ‘natural pretreatment’ I mentioned above.

You’ll remember that I collected seed from two different individual rowans: a tree on Whitwell Moor and a tree above Oaken Clough. I kept each seed collection separate to find out if there is any difference in growth or form between the seedlings of the two trees. I also divided each collection into thirds so that the seeds of both trees will undergo all three of the pretreatment methods recommended by Growing trees and shrubs from seed. I’ve provided an abridged version of each of those methods below:

A. “Easy: natural (outdoor) pretreatment / sowing with medium”

1. Prepare a moisture retaining medium by mixing one part organic material (such as peat or decomposed leaf litter) with one part coarse particle material (such as sand or grit).

2. Mix one part seeds with one part moist medium and place in a container which is open to rainwater at the top and has drainage holes at the base.

3. Pretreatment: place container outdoors for thirty (16 – 30) weeks, positioned so as to receive exposure to seasonal temperature changes whilst avoiding daily temperature fluctuations.

4. Inspect seeds regularly (weekly to fortnightly) and if necessary re-moisten the stratification mix or remove decaying seeds to prevent the spread of fungal infections.

5. Remove and sow germinating seeds (or sow all seeds when 10% have begun to germinate).

A. On Saturday I filled two small plant pots with a one part compost, one part sand mix. Into one pot I mixed a third of the Whitwell Moor seeds; into the other I mixed a third of the Oaken Clough seeds. I’ve placed the two pots outside where they are open to rainwater but should avoid large fluctuations in daily temperature. There they shall remain until spring. Sixteen to thirty weeks from the 10th of October gives us a planting window open from the 30th of January to the 8th of May. I’ll probably plant all of the Set D rowan seeds proper in March.

B. “Moderate: artificial (temperature controlled) pretreatment with medium”

1. Prepare a moisture retaining medium by mixing one part organic material (such as peat or decomposed leaf litter) with one part coarse particle material (such as sand or grit).

2. Mix one part seeds with one part moist medium and place in a container, leaving a gap in the top.

3. Pretreatment: two (2 - 4) weeks warm followed by thirty (16 - 30) weeks cold. Use the main compartment of a refrigerator for the cold phase.

4. Inspect seeds regularly (weekly to fortnightly) and if necessary re-moisten the stratification mix or remove decaying seeds to prevent the spread of fungal infections.

5. Remove and sow germinating seeds (or sow all seeds when 10% have begun to germinate).

B. On Saturday I filled two empty yoghurt pots with a one part compost, one part sand mix. Into one pot I mixed a third of the Whitwell Moor seeds; into the other I mixed a third of the Oaken Clough seeds. I’ve placed the two open-topped pots in the fridge where I’ll ensure that they remain moist until spring.

C. “Skilled: artificial (temperature controlled) pretreatment without medium”

1. Place seeds in a loosely-tied woven bag and rinse / soak in cold (+4°C) water for forty-eight hours to remove any chemical inhibitors.

2. Drain seeds in a sieve to obtain imbibed, surface dry seeds.

3. Transfer seeds to a polythene bag. Leaving an air gap above the seeds, loosely tie the neck of the bag with a finger-sized hole to permit gaseous exchange but retard drying.

4. Pretreatment: two (2 - 4) weeks warm followed by thirty (16 - 30) weeks cold. Use the main compartment of a refrigerator for the cold phase.

5. Inspect seeds regularly (weekly to fortnightly) and if necessary re-moisten the stratification mix or remove decaying seeds to prevent the spread of fungal infections.

6. Remove and sow germinating seeds (or sow all seeds when 10% have begun to germinate).

C. On Saturday the 3rd of October I started separate 48-hour soakings of the Whitwell Moor and Oaken Clough seeds. I rinsed the seeds two or three times during the 48-hours. A week later (last Saturday), I transferred the surface-dry seeds to two small polythene bags and placed them in the fridge.

* * * * *

So there you go. Will the seeds make it through the winter? Will any of them germinate next spring? Will there be any difference between the Whitwell Moor and Oaken Clough seedlings? Which method of pretreatment will be the most successful? Only time will tell!!!


Posted in Dendrology + The treeblog trees





Flowers of the ash, the wild cherry, and the sycamore

Spring is in the air and flowers are everywhere. So far this year treeblog has carried posts on the flowers of the hazel, the alder, the larch, and the goat willow; also last week, a crab apple on the verge of flowering; and if I may whet your appetite for posts to come, have a sniff of these soon-to-be-flowering trees: the rowan, the horse chestnut, the birch, and the hawthorn. What a bounty! What a feast! In today’s post: the flowers of the ash, the wild cherry, and the sycamore.

Cherry blossom.

The wild cherry or gean (Prunus avium) is a spectacular sight at this time of year as whole trees are covered with white flowers - the magnificent cherry blossom. All wild cherry flowers are hermaphrodite, each flower having a single style (♀) surrounded by several stamens with orange anthers (♂). By mid-summer, the bee-pollinated flowers will have developed into small red then red-black fruits; they are eaten by birds.

Cherry blossom at sunset.

These three wild cherry photos were taken yesterday evening in the Ewden Valley.

Ash flowers.

On the flowering front, the wind-pollinated ash (Fraxinus excelsior) is a bewildering, polygamous mess. From my Trees of Britain & Northern Europe (Mitchell, 1974):

Total sexual confusion: some trees all male, some all female, some male with one or more female branches, some vice versa, some branches male one year, female the next, some with perfect [hermaphrodite] flowers. Male flowers in dense globular bunches along shoots of previous year, purplish then dark red in bud, open yellow with slender anthers in early April well before leaf-buds; female flowers similar but open more widely into a filigree of purple then pale green.

and from my Trees of Britain & Europe (Aas & Reidmiller, 1994):

Flowers: Apr-May, before the leaves open, trees may be monoecious or dioecious, and the flowers hermaphrodite or unisexual, arranged in many-flowered panicles, at first upright, but later drooping, at the tips of the previous year’s growth. Individual flowers are inconspicuous and lack petals [and sepals]. Stamens 2(3), are brownish-red to violet; ovary has 2-lobed stigma.

Ash flowers.

I’m having difficulty discerning whether the ash flowers in my photos are male, female, or perfect, a problem possibly compounded by the flowers perhaps being past their best. With help from this this excellent page by Eva Wallander, I’m fairly sure the pinkish-red-headed parts are anthers (♂), but I’m not at all sure whether the black-headed parts are stigmas (♀) or just anthers that have already lost their pollen. If you can help me out, please email or leave a comment.

These three ash photos were taken on Friday.

Sycamore flowers seen yesterday on a tree in the Ewden Valley. Most local sycamores hereabouts are a little behind it with their inflorescences.

Figuring out which parts of a sycamore inflorescence are male and which are female sounds like another pain in the ass! From a paper by Binggeli (1990):

In Sycamore, Acer pseudoplatanus L., all flowers are functionally unisexual and appear sequentially on a single inflorescence… In a single inflorescence the sex of sequentially opening flowers may differ more than once in time, and de Jong… described eleven different modes of sex expression within an inflorescence…

and from Rusanen & Myking (2003):

The reproductive system is complex. The majority of flowers are morphologically hermaphrodite, but all flowers are functionally unisexual. In each inflorescence there are both male and female flowers – but the number of male flowers is higher, and the duration of the male flowering sequence is always much longer than that of the female sequence. At the tree level, half of the individuals function predominantly as male or female, but there may be some annual variation in sex expression. Flowers are a vital source of pollen and nectar for bees and bumble bees, which are the primary vectors for pollination. A small proportion of the flowers are also pollinated by the wind.

Sycamore leaves illuminated against the sky yesterday afternoon.


References

Aas, G. and Riedmiller, A. Translated by Walters, M. (1994). Trees of Britain & Europe. HarperCollins Publishers. – A Collins Nature Guide.

Binggeli, P. (1990). Detection of protandry and protogyny in Sycamore (Acer pseudoplatanus L.) from infructescences. Watsonia, 18, 17-20.

Mitchell, A. (1974). Trees of Britain & Northern Europe. HarperCollinsPublishers. – A Collins Field Guide.

Rusanen, M. and Myking, T. (2003). EUFORGEN Technical Guidelines for genetic conservation and use for sycamore (Acer pseudoplatanus). International Plant Genetic Resources [Rome]. Available from: http://www.ipgri.cgiar.org/publications/pdf/853.pdf [Accessed 26th April 2009].


Posted in Dendrology





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