Monday, 29 September 2014

Looking close up

Sometimes the garden can seem, at first glance, to be a bit less colourful and exciting than we might like. However, it turns out that there are all sorts of interesting things to see if we just go closer to the plants and have a good look. The plant below is a heather. It looks very beautiful and intricate close-up. 

The photo below shows how this same plant looks from only a foot away, so in this case it really is worth while getting up close for a proper look. 

What do you see in your garden, if you look really close-up?

Thursday, 25 September 2014

Why are strawberry seeds on the outside of the fruit: part 2.

Yesterday we formed a hypothesis about why strawberry seeds are on the outside of the fruit, when apple seeds are on the inside. 

Today we are going to have a look inside the strawberry flower and see if the anatomy backs up our theory. 

Below is a cross-section of a strawberry flower. The sexual organs are in the centre, with the female organs held on a tall column of tissue. The male organs are arranged in a ring around the female organs, and four of them are visible in this photo. The petals and sepals can also be seen flanking the male organs. 

The tall column in the centre is the part that will expand massively to make the strawberry fruit that we are so used to eating. The little green organs that sit all over the column are the many individual female organs. Each one of these tiny female organs has an ovary at the base and can produce one seed in the ovary.

The image below shows a close-up of this area of the flower. We can now clearly see each female organ, with a bean-shaped ovary at the base, a tall style reaching up, and the stigma at the top, where pollen will be deposited. It is very obvious from this photograph that that the ovary does indeed sit on the outside edge of the tissue that will later develop into the bright red strawberry fruit tissue. 

The photograph below shows a cross-section of the same small green strawberry that we looked at yesterday. As we can see, the fruit tissue has already increased hugely in size, and the seeds are already fairly mature, and sitting on the outside of the fruit. 

The photograph below show the fully mature ripe fruit in cross section. By this stage, the fruit tissue has grown even more, and the seeds are still visible on the outside edge. Small white lines of tissue are visible reaching out to each seed, and i assume that these are lines of vascular tissue taking food and water to the seed. This is just an assumption and I have not verified it.

So there we are. The inside of the strawberry flower seems to confirm our hypothesis that seeds grow on the outside of strawberries, because the ovaries sit on the outside of the nascent fruit tissue in even in the flower.

Wednesday, 24 September 2014

Why are strawberry seeds on the outside?

Why do strawberries have seeds on the outside, when apples have seeds on the inside? I wonder that every time I see a strawberry. Lets have a look and see what's going on. 

Below is a strawberry flower. In the centre is a large green blob covered in things that look like tiny green hairs. The hair-type things are the stamens and there are *lots* of them.

The carpels are the female part of the flower, on which pollen is deposited by insects. At the base of each carpel is an ovary containing an egg cell. The egg cell will be fertilized by the sperm that comes from the pollen. Together the fused pollen and sperm cells will develop into a seed. 

That means that for each of these tiny green hairs we will get one seed. So that explains why there are such a lot of tiny seeds. But why do they end up on the outside of the strawberry?

Well now we have to use our imaginations a bit. The critical question, as we recall, is why are apple seeds on the inside of the apple when strawberry seeds are on the outside? 

Lets think of the tasty part of the fruit as a big blob of tasty playdoh. Even in the newly opened flower, the very beginnings of this tasty playdoh are already present. In the strawberry's case, it seems to me that the ovaries just happen to be on the outside of the miniscule blob of playdoh, and so that's where the seeds develop. I assume, conversely that the apple ovaries are inside the blob of tiny blob of playdoh that is already present in the flower, and so when the apple develops, the seeds will be on the inside. Apples contain far fewer seeds, because their flowers have far fewer stamens.

These are my assumptions about the system. Tomorrow we will cut open a strawberry flower to test whether my assumptions are right.

So what happens when the flower starts to develop into a strawberry? First, the fused egg and sperm cells develop into a seed. At the same time the tasty fruit tissue develops and becomes larger. The photo below shows a tiny strawberry with its new green seeds and green strawberry tissue gradually developing. As the seeds mature, the fruit tissue enlarges and takes on its mature shape. 

A few days later, the fruit tissue is becoming larger and less green, while the seeds stay the same size and gradually get further apart. 

Finally the fruit tissue matures and takes on the rich red colour, telling us all that it is ready to eat. The seeds are sill visible on the surface, but are now much less prominent and much smaller in proportion to the mature fruit. 

So now we know. Strawberry seeds develop on the outside of the fruit, because the ovaries are on the outside of the rudimentary fruit tissue, even when the flower opens. In apples, conversely, the ovaries are right inside the fruit tissue, even at the time when the flower opens. 

Next time we look at a flower on a strawberry plant or apple tree, we can take careful note of the number of stamens. We know that we will be seeing just the same number of seeds on the fruit later in the year. We know exactly where they will be, and why. 

Just in case you were wondering, several strawberries were eaten during the making of this blog post. 

Wednesday, 17 September 2014

Bird Cherry Ermine

The Bird Cherry Ermine (Yponomeuta evonymella) do an amazing thing in the park near us every year. They colonise a whole row of Bird Cherry (Prunus padus) trees, eat all the leaves, and drape the trees all over in white webs, so that the trees resemble snowy Christmas trees. Below are some photos of the most recent colonisation.

Initially the trees look just like any other tree in summer - covered in leaves. Then the eggs are laid on the trees, and hatch into caterpillars. The caterpillars are there in their thousands and eat all the leaves completely away, so that not a single fragment of leaf is left.

In the distance the trees just look white. 

In close-up we can see the thick white webs on the twigs of the tree, and the caterpillars swarming all over them.

At the base of the tree, the webs fan out and the caterpillars can be seen marching away towards, what they hope is the next tree. They usually have to dodge round a bunch of curious children and lots of adults with cameras.

In the photo below you can see a grey area on the base of the trunk. This is a big pile of caterpillars. There are thousands of them on each tree.

The caterpillars do this for maybe a month or two each summer, and then they all vanish away to get on with their lives, and all of the trees' leaves grow back. A few weeks later, there is no sign at all that the caterpillars were ever there.

Tuesday, 16 September 2014


The plant below is Lunaria annua, better known as "Honesty". 

This is a beautiful flower, easy to grow, and very forgiving to the novice grower. It self-seeds freely and fills the garden willingly with flowers, with very little effort from the gardener. 

We all know the honesty plant when we see it. It is the one that produces these amazing seed pods, which are completely transparent. Initially the pods are green, but as they mature, it is possible to peel off the green outside layers, and reveal the beautiful translucent section, with the seeds visible in the middle. 

Honesty lives for two years, flowering in the second year, but once a population is established in the garden it self-seeds so freely that the garden is never without these flowers. 

What could be better?

Sunday, 7 September 2014

Composite flower developing

We previously looked at the parts of a composite flower, and in this page we're going to look at the development of the same flower. 

This photo shows the immature flower in close-up. As you can see the miniature flowers in the centre are maturing at different rates. The outer flowers are already mature, but the central flowers are still immature, with the male organs apparent, but the female organs still hidden. 

Immature flower of Osteospermum 'Tresco Purple'

This flower (below) is slightly more mature, and all of the tiny flowers in the centre have reached maturity, so that all of the female organs are all clearly visible.

Mature flower of Osteospermum 'Tresco Purple'

This developmental sequence is rather similar to that seen in the previous post "Guess what's going to be!"

Parts of a composite flower

We previously had a look at the parts of a simple flower, and in this post we have a composite flower. 

In the simple flower there was a cluster of sexual organs in the centre of the flower. The female organ was in the centre of the cluster and the male organs were in a ring round about. The composite flower still has a cluster of sexual organs in the centre. However, this cluster of organs is made up of several tiny individual flowers. 

Osteospermum 'Tresco Purple'

The close-up below shows the cluster of sexual organs in more detail. If you look closely you can see that each tiny flower has a central female organ with a sort of yellow cross on the top. Surrounding the female organ are a number of male organs which each have a green top. Then surrounding the male organs are some very small white petals.

If you count the female organs (with the crosses) then you can see that there are very many tiny flowers. This is why the whole big structure is called a composite flower. It is composed of many little flowers, with just one ring of big mature petals round the outside.

That's all you need to know to understand composite flowers. Next time you see a daisy, you can now give it a knowing look. :-)