dumb cane.

Name: Dumb Cane or Dieffenbachia
"This plant that we have in our homes and
offices is extremely dangerous! This plant is
common in Rwanda. It is a deadly poison,
most specially for the children. It can kill a
kid in less than a minute and an adult in 15
minutes. It should be uprooted from
gardens and taken out of offices. If
touched, one should never touch his/her
eyes; it can cause partial or permanent
blindness."

The plant depicted in the photograph is in fact a dieffenbachia, a species commonly used as a potted house plant because of its attractive appearance and its suitability for indoor, low light intensity growing environments. Dieffenbachia is indeed poisonous to humans and animals if parts of the plant are ingested. Dieffenbachia is also known as "Dumb Cane" because of the toxic effect it can have on the mouth and tongue if chewed.

However, this warning quite significantly exaggerates the risk of death associated with dieffenbachia poisoning. The results of dieffenbachia poisoning are normally not life threatening and victims usually make a full recovery. Given that eating the plant may potentially cause swelling severe enough to block the victim's airways, death is a possible result. However, research indicates that actual fatalities in humans are extremely rare. Certainly, there are no credible medical reports that back up the suggestion in the warning message that death is a common and very rapid result of dieffenbachia poisoning. An article discussing caladium, dieffenbachia, and philodendron plant poisoning published on the Emedicine website notes:

Patients with history of oral exposure (chewing and/or swallowing) have been reported to have severe swelling, drooling, dysphagia, and respiratory compromise, but this is not common. In a large retrospective study of 188 patients with plant oxalate exposure, all cases were determined to be minor and all resolved with minor or no treatment. Patients can also experience dermal and ocular exposure, resulting in contact dermatitis or keratoconjunctivitis. Symptoms that result from these routes of exposure also appear to resolve with supportive care. The serious complication of aortoesophageal fistula following ingestion of a dieffenbachia leaf in a girl aged 12.5 years has been described in a single 2005 case report. The girl recovered following surgical intervention.

And, the claim that rubbing your eyes after touching the plant can cause permanent blindness also seems to be an exaggeration. The Emedicine article notes that "Ocular exposure may result in eye pain, redness, and lid swelling", but makes no mention of permanent blindness. Other medical articles describe dieffenbachia induced corneal injury but again make no mention of permanent blindness.

While the warning message is overblown and inaccurate, it should be stressed that ingesting dieffenbachia can certainly cause a number of distressing and painful symptoms. Information about dieffenbachia poisoning published on the Medline Plus website records the following poisoning symptoms:

• Burning in mouth or throat
• Damage to cornea of the eye
• Diarrhea
• Eye pain
• Hoarse voice
• Nausea or vomiting
• Swelling in mouth or tongue

It should also be noted that dieffenbachia related poisoning among household pets does regularly occur and in some cases has resulted in the death of the animal.

Given that it is actually quite important that householders are aware that their dieffenbachia plants are potentially poisonous, especially if they are parents or guardians of younger children or have pets, the email does have some merit as a warning. Unfortunately, the email significantly erodes its potential usefulness as a cautionary tale by so blatantly misrepresenting the potential danger of the plant. Another quite serious flaw in the warning message is that it does not actually include the name of the plant under discussion. Some versions do not even include the image of the plant - which incidentally was apparently "borrowed" from the Lahore Nursery website for use in the message - thus rendering the warning virtually useless.

Why trees can't grow taller than 100 meters?

TYPICALLY, the taller the tree, the smaller its leaves. The mathematical explanation for this phenomenon, it turns out, also sets a limit on how tall trees can grow.

Kaare Jensen of Harvard University and Maciej Zwieniecki of the University of California, Davis, compared 1925 tree species, with leaves ranging from a few millimetres to over 1 metre long, and found that leaf size varied most in relatively short trees.

Jensen thinks the explanation lies in the plant's circulatory system. Sugars produced in leaves diffuse through a network of tube-shaped cells called the phloem. Sugars accelerate as they move, so the bigger the leaves the faster they reach the rest of the plant. But the phloem in stems, branches and the trunk acts as a bottleneck. There comes a point when it becomes a waste of energy for leaves to grow any bigger. Tall trees hit this limit when their leaves are still small, because sugars have to move through so much trunk to get to the roots, creating a bigger bottleneck.

Jensen's equations describing the relationship show that as trees get taller, unusually large or small leaves both cease to be viable (Physical Review Letters, doi.org/j6n). The range of leaf sizes narrows and at around 100 m tall, the upper limit matches the lower limit. Above that, it seems, trees can't build a viable leaf. Which could explain why California's tallest redwoods max out at 115.6 m.

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How Bluetooth Works

Bluetooth networking transmits data via low-power radio waves. It communicates on a frequency of 2.45 gigahertz. This frequency band has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM).

A number of devices that you may already use take advantage of this same radio-frequency band. Baby monitors, garage-door openers and the newest generation of cordless phones all make use of frequencies in the ISM band. Making sure that Bluetooth and these other devices don't interfere with one another has been a crucial part of the design process.

 

One of the ways Bluetooth devices avoid interfering with other systems is by sending out very weak signals of about 1 milliwatt. By comparison, the most powerful cell phones can transmit a signal of 3 watts. The low power limits the range of a Bluetooth device to about 10 meters (32 feet), cutting the chances of interference between your computer system and your portable telephone or television. Even with the low power, Bluetooth doesn't require line of sight between communicating devices. The walls in your house won't stop a Bluetooth signal, making the standard useful for controlling several devices in different rooms.

Bluetooth can connect up to eight devices simultaneously. With all of those devices in the same 10-meter (32-foot) radius, you might think they'd interfere with one another, but it's unlikely. Bluetooth uses a technique called spread-spectrum frequency hopping that makes it rare for more than one device to be transmitting on the same frequency at the same time. In this technique, a device will use 79 individual, randomly chosen frequencies within a designated range, changing from one to another on a regular basis. In the case of Bluetooth, the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of the radio spectrum. Since every Bluetooth transmitter uses spread-spectrum transmitting automatically, it’s unlikely that two transmitters will be on the same frequency at the same time.