Substances that inhibit germination appear to be almost as various as the plants that make them, and their chemistry is equally diverse. Some of them are among the oldest and best-known drugs, stimulants and poisons in the armamentarium of medicine. The alkaoid strychnine is one. Penicillin, an unsaturated lactone, is another. Many of the germination inhibitors are also insecticides. For the most part they are cyanogens, organic acids, unsaturated lactones, aldehydes, alkaloids and the essential oils. It is reported that even the slightest smear of oil from lemon peel, for example, will prevent the germination of wheat in a dish of otherwise fertile soil.

Inhibitors tend to concentrate in parts of a plant according to function. In the case of leafy vegetables, such as cabbage ft and lettuce, they are found in the leaf coat. They are concentrated in the leaf sap of spinach, in the bulb of the onion and garlic and in the root of the carrot and the horseradish. In apples and pears are stored in the pulp of the fruit; in tomatoes they are stored in the juice. Their function in fruits is to delay germination until after the fruit has fallen and decomposed into soil nutrient. The inhibitors are then leached away by rain in preparation for the new crop.

Some inhibitors are built into the seed, and not many of these have been investigated. Last fall Michael Zimler, a high school student in Roslyn Heights, N.Y., was casting about for a science-fair project and hit on the idea of setting up an experiment to learn if the seed of Merion bluegrass, the popular lawn cover, contains an inhibitor and, if so, how effective it is against the germination of other plants.

"I started out," Zimler writes, "on the assumption that the grass seed contains an inhibitor that could be extracted by water in sufficient concentration to be detected. The apparatus used in the experiments was assembled for the most part from materials found around the house: assorted glasses, bottles, jars, Saran Wrap and toy balloons. The specimens exposed to the inhibitor included the seeds of radish, lima bean, green pea, cucumber, corn, morning glory, sunflower, zinnia and gourd. Tests were also run on yeast and bread mold. Packets of fresh seeds were bought from a local store that deals in garden supplies, and the yeast, in dry form, came from the corner grocery. Three germinating media were used: white blotting paper, washed sand and a mixture of washed sand and peat moss.

"To make the extraction I put a half-pound of grass seed in a half-gallon jar, added a quart of tap water and let the mixture stand overnight. I stirred it occasionally before bedtime and again in the morning. At the end of 12 hours the liquor was filtered through a square of nylon mesh cut from an old stocking that had been washed with soap and thoroughly rinsed.

"Enough tap water was added to the filtered liquor to make up two quarts. This was poured into smaller jars, which were wrapped with aluminum foil to keep out the light and stored at room temperature. Within a few days the extract spoiled, turned cloudy and developed an offensive odor. I made up another batch the same way but stored it in the refrigerator at approximately 42 degrees Fahrenheit. This suppressed the growth of microorganisms, and the extract remained clear throughout the period of the experiments.

"My first attempt to germinate seeds also failed. Several conical dessert glasses were lined with white blotting paper. The paper in half the glasses was saturated with the extract; the paper in the other glasses, which were to serve as controls, with tap water. The dry seeds from the packets were inserted between the blotting paper and the glass so that sprouts could be observed without disturbing them. The number of seeds planted in each glass varied from 12 to 50, depending on the variety and size. The arrangement seemed sensible, particularly because it would be easy to keep the paper moist. It turned out, however, that only a small area of each seed made contact with the paper and the seeds did not get enough moisture to sprout.

"The next batches were planted in sand. The glasses were cleaned, dried and nearly filled with dry sand. The seeds were soaked overnight, the controls in tap water and the test specimens in extract, and embedded lightly in the sand. Thereafter the sand was kept moistened with either water or extract as appropriate and maintained at room temperature. Within a week a high percentage of all the controls had germinated with the exception of the lima beans.

"The presence of an inhibitor was strikingly apparent, particularly in the cases of cucumber, green pea and radish. Within a week 58per cent of these seeds sprouted in the control plantings but none in the sand to which grass extract had been added. Plants showing maximum resistance to the inhibitor were sunflower, corn, morning glory and zinnia, in that order. The controls, in the case of these four plants, also exhibited more vigor than plants that were susceptible to the inhibitor. Ninety-four per cent sprouted in tap water. The results are summarized in the accompanying table [right], and also by graphs for morning glory, radish and zinnia. The number of seeds in the test planting is plotted against growing time in days [see Figure 1 ].

"I performed a similar experiment to test the possible effect of the inhibitor on a fungus, which does not reproduce by seed. The most readily available fungus that can be procured in a relatively pure strain is ordinary baking yeast. Most yeasts can live and grow only in a solution that contains sugar or substances that are easily converted into sugars. Such substances are present in wheat flour.

"Two packages of active dry yeast were dissolved, one in eight ounces of warm inhibitor solution and the other, for a control, in eight ounces of warm tap water. Each yeast solution was then mixed with eight ounces of wheat flour, and the doughs were set to rise in a warm oven for one hour. The dough that was prepared with inhibitor appeared to rise more rapidly and to a somewhat greater volume than the control, but the rates were difficult to measure.

"Accordingly a second experiment was set up in which the influence of the inhibitor was judged by the amount of carbon dioxide liberated by fermentation. A package of yeast was divided into equal parts and each part was softened, one with two ounces of inhibitor liquor and the other with two ounces of tap water. After standing undisturbed at room temperature for four hours the yeast was further diluted so as to make 10 ounces of inhibitor solution and 10 ounces of control respectively. Four tablespoons of granulated sugar had been added previously to each of the diluting solutions as nutrient. The solutions were transferred to 12-ounce soda bottles and capped by rubber balloons from which the air had been squeezed. The capped bottles were then immersed to their necks in a pan of warm water (about 100 degrees Fahrenheit) and incubated for two hours. To maintain the temperature a small amount of cooled water was dipped from the pan occasionally and replaced by hot water. Carbon dioxide, evolved by fermentation, inflated the balloons. The volume to which the balloons expanded could be calculated approximately from measurements of their height and diameter. The calculated volume was taken as an index of the effectiveness of the inhibitor. The 'inhibited' yeast turned out to be approximately 30 per cent more active than the control! Germination inhibitors, according to the literature, can affect organisms, both plant and animal, in various ways according to dosage and the nature of the organism. Caffeine, for example, will act as a stimulant, a poison or a germination inhibitor, depending on the amount of caffeine administered, how and to what. Perhaps the substance in Merion bluegrass acts as a stimulant for cultured yeast. On the other hand, it is possible that the inhibitor in bluegrass has no effect on the yeast; that nutrients washed from the seed account for the accelerated growth.

"I have not had time so far to check these guesses by experiment. The tests that have been described were made last year while I was a sophomore and are being continued this year on a number of molds and bacteria. Before the runs are finished I hope not only to resolve the question of whether the extract can function as a stimulant but also to identify the inhibiting substance. In several closely related plants the inhibitor has been identified as coumarin, an unsaturated lactone that is available commercially. I intend to make simultaneous runs with coumarin and Merion bluegrass inhibitor on a number of organisms and, having tabulated the results, to analyze the two solutions by paper chromatography. If a chromatographic zone of the extract migrates at the characteristic rate of coumarin and exhibits the same inhibiting properties, the extract will probably be coumarin. If no zone migrates at the rate of coumarin, the extract will be compared with other known inhibitors."

Amateur telescope makers who reach the age when physical comfort and convenience take precedence as design criteria over cost usually settle on an instrument that features a fixed eyepiece. The first mounting of this type was made 42 years ago by the late Russell W. Porter, one of the founding fathers of amateur telescope making. Telescopes must be movable so that the observer can point the objective lens or mirror toward any desired region in space and follow selected objects across the sky. With conventional telescopes the whole instrument moves, and the observer has to move too. The eyepiece is mounted rigidly to the tube, either at the rear end in the case of refracting instruments or on the side of the tube at the front end in the case of Newtonian reflectors. In both designs the eyepiece moves with the tube, and it can get itself into some distressingly neck-craning positions. To reach all parts of the sky the tube must rotate in two planes: up and down and from side to side. In making an analysis of these motions Porter observed that the point at which the planes intersect always stays fixed. Why not locate the eyepiece at this point? Mechanically the two axes that are normal to the planes must be offset to provide space for bearings. But they can be brought together optically by equipping the mechanism with a pair of prisms, one centered in each axis. In the reflecting telescope, Porter located one of the two prisms on the optical axis of the tube to bend the focused rays at a right angle through a hollow bearing on which the telescope turns up and down. He centered the second prism on the polar axis, on which the telescope turns from side to side. In this location the prism bends the rays into the fixed eyepiece. In astronomical telescopes the polar axis parallels the axis of the earth. Porter's design enables the observer to look down this axis, and at the latitudes of the U.S. the angle of view is most comfortable.

But the design contained one flaw that troubled Porter. The use of hollow bearings meant that the diameter and the loaded surfaces of the bearings had to be large. Moreover, the tube had to be supported near one end and counterbalanced in one plane by a weight supported on a beam that would also provide equilibrium in the second plane. The beam could not be allowed to sweep through the observer's position. Porter solved this geometric puzzle by simply fastening a rod to the front end of the telescope, bending it over the observer's head and hanging a weight on the outer end. This counterbalanced the tube, but it also loaded the bearings with a force in the form of a couple that made the instrument hard to turn. Some years later he suggested that the loads in each axis could be counterbalanced separately by substituting a crescent-shaped slug of lead for part of the weight at the end of the hooked beam and supporting the slug by a short beam that would swing between the observer and the instrument. This stratagem would eliminate the coupling force. "I have never seen such a weight, nor made one except on paper," Porter wrote a few years before his death in 1949, "but I would like to see it tried out."

A telescope that incorporates the idea has now been constructed by Ralph Sangster of Brighton in South Australia, who reports that it works beautifully. "I set out to build an instrument designed specially for making studies of lunar and planetary detail," he writes. "During such studies the observer must keep his eye glued to the instrument for hours on end. If possible, all control knobs and switches should be within easy reach and operable by touch alone. A telescope of the fixed-eyepiece type meets these requirements, and I decided to build one incorporating the revisions that Porter suggested.

"To eliminate guesswork from the optical assembly I also decided to make a long-focus instrument. At focal ratios of f/12 and higher, spheroidal mirrors operate about as well as paraboloids and very much better than the poor paraboloids that an inexperienced amateur may make. A good spheroid is almost as difficult to figure as a paraboloid. But it is much easier to test. You may not wind up with a perfect spheroid but at least you know how much it departs from perfection. Moreover, a big focal ratio gives reasonable magnification for observing planets without the use of tricky and expensive eyepieces. The aperture of my mirror is eight inches and the focal length 100 inches. A one-inch eyepiece therefore gives a magnification of 100 diameters.

"The pier that supports the instrument, the observer's platform and the seat is an eight-foot length of steel pipe, eight inches in diameter, filled with 300 pounds of concrete and anchored upright by a pipe flange that is bolted to an 1,100-pound slab of concrete [see Figure 3]. The observatory is 20 feet square and nine feet high. If constructed of conventional materials, it would have cost at least $1,500. The actual cost was just a little over $100- plus a lot of labor. Essentially it is a basin scooped out of the sandy ground in my back yard and walled with stone quarried from a nearby outcrop. The observatory is roofed with corrugated sheet iron on a wooden frame that rolls on a pair of elevated rails. The level of the roof is two feet above the ground and allows the telescope to be pointed within 10 degrees of the horizon.

"To carry out Porter's suggestion for balancing the instrument, a 60-pound weight was first suspended by a bracket at the outer end of the tube. The bracket was bent just enough to center the combined mass of the tube and counterweight on the declination bearing. This minimized torque around the declination axis. A thin crescent of lead was then cast in a mold of sand and attached to a beam that also served as a wheel for rotating the instrument in right ascension, as shown in the accompanying drawing [right]. At our latitude the angle at which the wheel and counterweight are inclined provides eight inches of clearance between the apparatus and the observer.

"The assembly turns as smoothly as the dial of a bank vault and with little more effort. The mounting is fitted with a worm gear for attaching a clock to drive the tube in right ascension, and I believe that a conventional electric-clock motor will power it. The one-revolution per-minute shaft of the clock will be coupled through an idler gear to a five-to-one set of reduction gears. The output of the gears will drive a worm of 10 threads per inch that engages the 288 teeth of the right ascension worm wheel.

"My greatest satisfaction is in the comfortable bus seat. The seat is adjustable up and down, in and out, and is hinged like a rudder to the pier just beneath the southerly platform. The pier also supports side platforms, which come in handy when making periodic adjustments and fitting accessories to the instrument. The side platforms were made narrow so that they would not impede the movement of the tube. On stargazing nights visitors easily climb the short ladder to the observing seat, and the thrill of steering a telescope this large with the tip of a finger often makes it hard to get them down again."

Bibliography

AMATEUR TELESCOPE MAKING ADVANCED. Edited by Albert G. Ingalls. Scientific American, Inc., 1949.

PHYSIOLOGY OF SEEDS. William Crocker and Lela V. Barton. Chronica Botanica Company, 1953.

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