Birdsfoot Trefoil Takes Over

Birdsfoot trefoil is an attractive relative of a familiar group of species of clovers known as Trifolium, which includes red, white, Swedish, Dutch and nearly 300 other species. Like clovers, it is a useful plant. While it grows on roadsides, it helps control erosion. It feeds both wild animals (geese, deer and elk) and domestic ones, without bloating the latter. The actual genus of birdsfoot trefoil is Lotus, which includes less members than Trifolium, some of which may need to be reclassified. The rest of its name which designates its species is corniculatus, and it’s very similar to other species with the birdsfoot name: slender, alpine and smallflower.

Why is it called birdsfoot? At first glance, the flower looks like that of a pea, another member of the Plant kingdom’s 3rd largest family, Leguminosae, which, of course, includes the pea-genus (Pisum) along with Lotus, Trifolium and about 750 others. But if you look at mature birdsfoot flowers, their seed pods spread out in a plane and resemble a bird’s foot.

The plant first caught my attention in the 1980s on northern stretches of the 87 interstate highway headed to New York City. In Montreal, I had never seen it. A few decades later it began to appear sporadically in small patches in parks and abandoned fields. This year in July it has become so dominant in parks and big lawns, that from a distance, one could mistake them for dandelions. Here is a field I photographed in 2011 when white clover dominated, and the same field nine years later when birdsfoot trefoil reigns.

Why the change? White clover is best suited to soils which have good moisture-holding ability. Birdsfoot trefoil does better in dry soils. Given that Montreal had unusually arid months of May and June this year ( 33.6 and 46.4 mm of rain instead of the usual 81 and 87 mm), this could have contributed to the boom in the growth of corniculatus.

Occasionally, one will notice birdsfoot trefoil flowers that are orange instead of yellow. Older flowers occasionally take on the latter color. I thought of a couple of explanations. They do contain lutein which appears yellow at low concentrations and orange to red at higher concentrations. Presumably, with age, lutein accumulates. But beta carotene is also found in the plant, so if its content builds up, it could also be responsible for the color change.

The highly conjugated structure of lutein, C40H56O2 , is responsible for the yellow color of birdsfoot trefoil flowers.
Beta carotene, C40H56, is very similar in structure to lutein. The former replaces a hydrogen on each end-ring with hydroxyl, and the ring on the right is conjugated with the rest of the structure. This means less energy is required to excite its electrons, leading to a higher blue maximum absorption peak for beta carotene. That in turn leads to a reflection of more orange than yellow. (see graph below)


Fatty acids, α-tocopherol, β-carotene, and lutein contents in forage legumes, forbs, and a grass-clover mixture.Elgersma A, Søegaard K, Jensen SK.J Agric Food Chem. 2013 Dec 11

USDA Natural Resources Conservation Service.

The Audubon Society Field Guide to North American Wildflowers. Richard Spellenberg. Knopf. New York. 1987


How Could I’ve Forgotten Uncertainty?

In the late afternoon, after closing the lid on some chicken that I had just started to BBQ, I decided to empty the compost bin. Since the next day was compost and recycling collection day, I figured that I might as well roll out both bins to the curb. Then my neighbor walked by with his dog, Edgar Allen Poe. We started to talk about trees on the street, flooding issues and eventually about how numerous and vocal the birds have been this spring and early summer.

My neighbor pointed out that his cat who died over the winter had been a major bird killer. But I doubted it was merely a local effect. Several people I know have been enjoying the new hyperactivity of birds recently . In addition, we’re not far from the city’s major airport. With the COVID-19 lockout earlier in the year, and with the ongoing and drastic reduction in flights, the neighborhood has been a lot more quiet, making the birds more audible, perhaps even encouraging them to sing a little more.

“Air traffic was especially heavy from about to 3 to 6 PM. I would notice plane after plane when I’d be BBQing….OH SHIT….Sorry, Charley. I just remembered I have BBQ going!”

I ran inside and back out through the patio door, hoping that my wife had come to the rescue. But she was busy preparing the vegetables. It had been 25 minutes. I was expecting to find carbon instead of breasts on the grill, at least on one side. But when I lifted the lid, the sides facing me were white and the flip side was beautifully streaked and deep- brown. But the flames seemed weak. I quickly flipped all four pieces and re-closed the lid.Within a minute I heard the popping last gasp of the empty propane tank.

How could the gas have run out in less than half an hour? Given that we have guests coming on Sunday, after the last time I used the BBQ, I weighed the tank. It was 20 pounds. With a tare weight of 17 lb, that meant I had 3 lb or about 3 hours left at its maximum setting. Then I remembered that scales have uncertainties. And the uncertainties for the bathroom scale I used are especially dependent on the weight being measured. Furthermore, it had been difficult to get a reading from directly placing the propane tank on the scale. So I weighed myself with and without holding the tank, which of course, doubles the uncertainty. You can see from this data that a 3 pound(1.4 kg) measurement could easily have been in reality 0.2 kg!

From, Accuracy and consistency of weights provided by home bathroom scales. BMC Public Health. 2013; 13: 1194

I can’t wait to run into my neighbor again to tell him what happened after I had panicked for nothing, merely because I had temporarily forgotten about the concept of uncertainty.

How We Learned About Viruses and What They’ve Taught Us About Life

Viruses have been and continue to be a puzzle to solve, and the more we learn about them the more we learn about fundamentals of life in general. Until the electron microscope and the ultracentrifuge became available from 1935 to 1940, no one could see or chemically analyze a virus. But over 40 years earlier, the Russian botanist, Dimitri Ivanovsky made the first major breakthrough. He learned that whatever was infecting tobacco plants was unlike bacteria in that it could not be trapped by a porcelain filter.

Martinus Beijerinck

In 1898, Beijerinck, a Dutch microbiologist, verified Ivanovsky’s experiments and introduced the term filtrable virus to describe a new classification of infectious agent. Soon clinicians realized that the same filtration property was shared by the agents that caused rabies, polio , herpes simplex, and vaccinia, which had been used for smallpox vaccination. Beijerinck and others also discovered that viruses could not be cultured without living cells. Unlike bacteria, they needed hosts to reproduce.

Eventually, electron micrographs revealed to scientists that viruses came in various shapes and with different surfaces. Oblique evaporation of a thin film of metal over the preparation created a three-dimensional effect , leading to new information about the heights and shapes of viruses. Notice in the following images that vaccinia is rectangular, polio, spherical and tobacco virus is rodlike. (From Robley C. Williams , Ralph W. G. Wyckoff. Science  08 Jun 1945.)

One of the most important insights gained from studying viruses was their composition and mechanism of reproduction. At first it seemed that they were composed of only proteins, but then it was realized that the protein was always accompanied by nucleic acids(DNA or RNA), and that nucleic acids acted as the hereditary material. This also turned out to be true for all living cells.

The idea came from the Alfred Hershey-Martha Chase experiments of 1952. They demonstrated that the genetic material of a phage (a virus that infects bacteria) is DNA, not protein.

The clever experiment used two sets of T2 bacteriophages. In one set, the protein coat is labeled with a radioactive isotope of sulfur (35S), not found in DNA. In the other set, the DNA was labeled with radioactive phosphorus (32P), not found in protein. Only the 32P ended up in the E. coli bacteria, revealing that DNA was the agent needed to make new virus. Later in the decade, after the Chase experiments had inspired Franklin, Crick and Watson to elucidate DNA’s structure and method of replication, two research groups separated the tobacco virus’ protein coat from its RNA interior, and discovered that only the latter was capable of producing symptoms in tobacco leaves.

In 1970, Temin and Baltimore realized that some RNA viruses, retroviruses, could inject their RNA into host cells’ DNA. They do so by using the enzyme reverse transcriptase. The discovery that the information in RNA could be relayed to DNA meant that genetic information is not only transferred in one direction, from DNA to RNA, as previously assumed, but also in the opposite direction.

In more recent decades, virologists have slowly come to realize that only a minority of viruses cause disease. Most are innocuous, some are definitely beneficial, and others are indispensable to their hosts. I explored that theme here.