Sonntag, 17. April 2011

Article of the week: Attack of the cones

My first real article of the week (besides my little excursion in Düsseldorf) is about cones I want to show you pictures of some cones I collected during the last months. But first of all I want to make a little introduction to the wonderful world of cones.

What is a cone exactly? I'm sure everybody has seen at least one cone in his life. They hang from trees or lying on the ground, in the woods and on the street. They are a popular decoration during the christmas season.

But why make the trees this cones? What is their function? In short, cones are the reproduction organs of the conifers (giving this class the name “Coniferopsida”). You can distinguish male and female cones. Sometimes a tree has both of them which is called Monoicous. Sometimes a tree is pure female (having only female cones) or male (having only male cones), which is called Dioecius.

Male cones are responsible for the production of pollen. Because of the fact, that conifers using the wind to distribute their pollen, this male cones are often very small an fragile, which means, that they breaking up easily after sowing the pollen and vanished until next year.

The basic female cones, which should be the main topic here, consist of several ovules, which together form a ear like inflorescence. Every ovule is sitting at a small, short shoot. The complex of ovule and shoot is called “seed scale”, which stands in the axis of scale-like bract: the bract scale.

So bract and seed scales are the only protection for the ovule. As the ovule is otherwise naked, the coniferopsida are also known as Gymnopsermae (together with the Gentales and the Gingkoopsida); meaning "naked seeders".

During the pollination period the ovule forms a small drop: the pollination drop which grows through the input region of the ovule (Micropyle). The task of this drop is to capture the pollen, which came with the wind and pull them through the micropyle into the ovule, where pollination takes place.

After successful pollination, the ovule starts to grow. It becomes bigger and more woody. In this period, the seed scale starts to grow and often becomes bigger than the bract scale. In other cases, there are not two different types of scales e. g. at the Cupressacae). When ripe the bract scale seems only like a small film at the base of the seed scale.

Summarized a female conifer cone is a inflorescence of many small ovules, which are covers by a bract scale, a seed scale and sometimes with only one scale. After pollination, the seed scale starts two overgrow the bract scale and becomes hard and woody.

So that's enough theory for the day. Next I will show you some ripe, female cones of different conifers (and one non-conifer).

The first is a cone of one of the best known conifers of Germany: Picea abies L.

It is a very big oval cone indeed. Maybe you can see the sprial turns with the seed scales screwing to tip. The bract scales have vanished completely.

The next cone is from Pinus nigra J. F. Arnold, a tree a tree that is native to southern Europe, but also occurs in Germany as feral forest tree.

The cones have a typical pyramidal shape and are very big. The best character however are the black coloured bract scales (s. picture), through which the species is easily distinguished from the in Germany native forrest-pine (Pinus sylvestis L.)

The following picture shows also the cone of a pine, which is indigenous to North Americ and came to Europe during the 18th century. It's the cone of Pinus strobus L. (Eastern White Pine)

It's a striking cone, which differs great from the cones of Pinus nigra J. F. Arnorld. They are thinner, longer and bent a little bit. The bract scales have a dark brown colour.

American followers of this blog will know the next species for sure. It's Sequoiadendron giganteum (Lindl.) J. Buchholz, the good old giant sequoia. I found this cone in a botanical garden at the feet of this very impressing tree.

The cone is small and almost round or blunt oval. The scales (here we have only one scale, because it's a member of the Cupressaceae) are rhomboid shaped with a small notch.

My next cone should also be well known by Americans: Sequoia sempervirens (D. Don) Endl. or “coast redwood” in Englisch and the only member of the Sequoia genus (although Sequoiadendron and Metasequoia are often called “sequoia”).

The cones are small and have a long stalk. At it's surface, the scales has a small thin furrow.At first glance, cones of S, sempervirens can be confused with the cones of  Metasequoia glyptostroboides Hu et Cheng. Besides the fact that S. sempervirens is native to California and M. glyptostroboides to China, the cones of first one also are more flat at the top.

The last conifer of today is a very exotic one. Let me introduce you Cryptomeria japonica (L. F.) D. Don, native to eastern asia.

The most interesting feature of this very small, egg shaped cone are the small thornes at the back of the scale, giving the cone a rough scratchy surface. It's sitting at a small stalk.

The last plant of the day is not a member of a coniferopsida, but belongs to the real flowers. It's a member of the Magnoliaceae (Magnolias), a very primitive family of the flowers with big blossoms. I don't know the exactly name of this species, so I will call it Magnolia spp. (if you know the species, leave comment)

What you see here is the fruit of the Magnolia. It consists of many small and free carpells arranged around an axis. After pollination, the fruits become woody and form a fruit of several small fruits, that looks like a cone. In botany, such a fruit is called a follicle.

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