This edited article about the hydrangea originally appeared in Look and Learn issue number 170 published on 17 April 1965.

Hydrangea by F Edward Hulme

If you ever see a gardener potting a hydrangea plant like this one and mixing iron filings with the soil do not imagine that he is a victim of absent-mindedness!

The gardener will be well aware of what he is doing – because iron filings mixed with the potting soil of a red or pink hydrangea turns the flowers blue. It is a trick practised by gardeners on this attractive flowering shrub when they want to change their colour scheme.

After the iron filings are added the gardener waters the soil with alum at the rate of one teaspoonful dissolved in a gallon of rain water.

Actually, the iron filings method of turning pink hydrangeas blue has been superseded today by “blueing powders” which do the same job more efficiently when added to the soil.

Many different varieties of these small-petal plants were cultivated in China and Japan centuries before their introduction to Western gardens. European gardeners are particularly fond of the plant for their terrace tubs, and they make a splash of colour in a tub on the patio or veranda of a town flat.

Hydrangeas are grown by taking cuttings, inserted in potting soil between May and August. The pots should be kept in a propagating frame in a greenhouse or in a closed cold frame. On sunny days the cuttings should be shaded from bright sunlight.

When the cuttings are rooted they need some air, and soon the young plants will be ready for separate potting in compost. By autumn or early spring the plants will have grown to the point where they will again need re-potting.

Nearly all hydrangeas lose their leaves in winter and they need a certain amount of protection from severe weather. It is a good idea not to let them suffer a temperature below 45 degrees Fahrenheit.

In early springtime hydrangeas grow fast and this is the time when they enjoy a regular meal of weak liquid manure. With the proper treatment you can get a magnificent head of bloom in the plant’s first spring from cuttings rooted the previous May.

In summer the flower heads fade and as soon as this happens is the best time to prune the plants. In late summer and autumn the flower buds form at the ends of the shoots ready for the following spring, which is why it is important not to prune the plants after the summer is over. Many of them are quite hardy, and make large bushes outdoors.

This edited article about poisonous creatures originally appeared in Look and Learn issue number 1018 published on 12 September 1981.

Green, amber, red . . . we are all familiar with traffic lights, and understand that green is safe, amber a warning, and red emphatically means “Stop!” Traffic lights are a relatively recent invention, but warning colours are far from new, and have evolved over millions of years. In nature, vivid colours – particularly red – often warn of danger, and it can be as wise to stop well away from an animal or insect with bright warning colours as it is to obey the red traffic light.

In Britain there are few dangerous or poisonous creatures, but if you think carefully you might well recall some examples. The wasp’s bright yellow and black stripes warn of its nasty sting, just as the zig-zag pattern on the back of an adder hints at its venom. In contrast, the harmless grass snake is green. However, have you ever wondered why ladybirds are red and black, or why certain moths, such as the garden tiger and red underwing, have bright red underwings?

The answer, of course, is simple. Ladybirds are poisonous, and their colouring warns birds to leave them well alone. Starlings feed their young on insects, but in a study in Holland it was found that out of 16,484 insects taken to feed nestling starlings by their parents, only two were ladybirds, so their coloration really does protect them.

An interesting aspect of the ladybird’s defence is its ability to ooze blood from its leg joints when attacked. This is called reflex bleeding.

Ladybirds are not the only British beetles to display warning colours, for the cardinal beetle does so too. This crimson-red beetle receives its name from the similarity of its colouring to a cardinal’s robe; like the ladybird, it is also distasteful to birds.

Most moths, when at rest, have cryptic colouring which helps them merge with their background. However, certain species, when disturbed, suddenly reveal bright red underwings, which has the effect of alarming a predator.

This display is called flash coloration, and is often found among grasshoppers, cicadas, moths and butterflies. One of the best examples is the garden tiger, which is a common moth in Britain and often flies by day, even in bright sunshine. Glands in the tiger moth’s thorax secrete a poison, and birds soon learn to avoid this species.

This edited article about rodents originally appeared in Look and Learn issue number 155 published on 2 January 1965.

The Coypu and a water vole, large and small rodents

When we hear the word “rodent” we immediately think of rats. But the rat is only one of many different kinds of animals which zoologists class as rodents.

“Rodent” is a group name for about 2,000 species of animals distributed over nearly all parts of the world, including rats, mice and rabbits, and unfamiliar ones like the porcupines, the jerboa and the mink.

The name “rodent” comes from the Latin word rodo, meaning “I gnaw,” and it is this habit of constant gnawing that distinguishes the rodents from all other animals.

Unlike the horse and the cow, which chew their food, and the dog and tiger which tear it, rodents chop their way through their food in much the same way that a carpenter shaves off wood with a chisel.

Rodents do not have on each side of the jaw the large, fang-like teeth, called canines, of the dog and cat. Instead they have in front of the jaw powerful teeth called incisors, which are shaped like curved chisels – and are quite as sharp.

As fast as the tops are worn down by constant gnawing, they continue growing upwards from the roots.

If a rodent cannot have something to nibble at all the time, its incisors will grow to an extraordinary length.

Should an incisor break off, the one opposite to it goes on growing and eventually forms a curve round the animal’s head. The unfortunate rodent is then unable to open its mouth to eat and dies of starvation.

Sometimes when a top incisor breaks off, the bottom one will grow upwards until it pierces the animal’s skull and kills it.

It is this constant struggle to keep their incisors short and sharp that makes rodents so destructive. Most of their gnawing is not done for eating, but to prevent their teeth from growing too long and killing them.

We have selected three of the best pictures from our large collection of 19th and early 20th century educational trade cards.
The first picture shows the Battle of Tippecanoe.

The Battle of Tippecanoe

The second picture shows doll makers.

Dressing and painting dolls

The third picture shows Perroquets Aras and Fleur de la Passion.

Perroquets Aras and Fleur de la Passion

High-resolution scans of all educational cards can be found in the Look and Learn picture library.

We have selected three of the best pictures from our large collection of 19th and early 20th century educational trade cards.
The first picture shows the execution of the Earl of Essex in 1601.

Execution of the Earl of Essex, 1601

The second picture shows the burning of the books of Confucius.

The burning of the books of Confucius

The third picture shows the Highlands.

The Highlands

High-resolution scans of all educational cards can be found in the Look and Learn picture library.

We have selected three of the best pictures from our large collection of 19th and early 20th century educational trade cards.
The first picture shows the capture of Peking by the Mongols in 1215.

Capture of Peking by the Mongols, 1215

The second picture shows Bluebeard’s wife succumbing to temptation and unlocking the forbidden room.

Bluebeard's wife succumbs to temptation and unlocks the forbidden room

The third picture shows a picnic in Epping Forest.

The Picnic, Epping Forest

High-resolution scans of all educational cards can be found in the Look and Learn picture library.

We have selected three of the best pictures from our large collection of 19th and early 20th century educational trade cards.
The first picture shows the Galley of the Roman Emperor Caligula on Lake Nemi.

Galley of the Roman Emperor Caligula on Lake Nemi, Italy, 1st Century

The second picture shows Mount Etna.

Mount Etna

The third picture shows the submission of the Saxons to Charlemagne.

Submission of the Saxons to Charlemagne

High-resolution scans of all educational cards can be found in the Look and Learn picture library.

We have selected three of the best pictures from our large collection of 19th and early 20th century educational trade cards.
The first picture shows Aeneas at Dido’s palace.

Aeneas at Dido's palace

The second picture shows passengers boarding an airship.

Boarding the airship in London

The third picture shows a hurricane on Martinique.

Hurricane on Martinique

High-resolution scans of all educational cards can be found in the Look and Learn picture library.

We have selected three of the best pictures from our large collection of 19th and early 20th century educational trade cards.
The first picture shows Apollo’s chariot.

The Chariot of the Sun

The second picture shows the Siege of Tientsin during the Boxer Rebellion, China, 1900.

Siege of Tientsin, Boxer Rebellion, China, 1900

The third picture shows Mexicans harvesting Vanilla pods.

Mexicans Harvesting Vanilla Pods

High-resolution scans of all educational cards can be found in the Look and Learn picture library.

We have selected three of the best pictures from our large collection of 19th and early 20th century educational trade cards.
The first picture shows the destruction of Saint-Pierre, Martinque, by the eruption of Mont Pelee in 1902.

Destruction of Saint-Pierre, Martinque, by the eruption of Mont Pelee, 1902

The second picture shows The Emperor Frederick II taking the crown of Jerusalem in 1229.

The Emperor Frederick II takes the crown of Jerusalem in the Church of the Holy Sepulchre, Sixth Crusade, 18 March 1229

The third picture shows the death of Jean-Francois de la Perouse in 1788.

Death of Jean-Francois de la Perouse, French naval officer and explorer, 1788

High-resolution scans of all educational cards can be found in the Look and Learn picture library.