( Originally Published 1943 )
Pollen History. Pollens have been described as being just so much yellow dust. In fact the name pollen means dust. When seen by the average individual pollens are observed in large quantities. As previously indicated, wind borne pollens are produced in huge amounts. Reports of pollen showers and pollen clouds are not unusual. Observers have described areas of the Alps in which the snow was colored with a yellowish tinge due to pine tree pollens. Thomen gives the following quotation from the New York Sun of August 19, 1930:
"Superstitious farmers of the Bordeaux vineyard region are firmly convinced that this summer's crops are going to be golden.
"The first `golden rain' of five years has fallen over the vineyards. The `golden raindrops' are glistening yellow, caused by clouds picking up yellow pollen from the pine forests of the Basque country and then letting the pollen fall in rain.
"The farmers have found that every year when the golden rain has fallen has been a good year for record crops."
With our knowledge that pollens are the male fertilizing elements for plants, we can readily understand the relation between "golden rains" and record crops.
On a scientific basis the true nature, appearance, and function of pollens has not long been understood. From carvings dating about 900 years B.C., the Assyrians were credited with being the earliest to recognize sex in plants. This by reason of sculptures (at present in the New York Metropolitan Museum of Art) showing figures of ancient Assyrians pollinating the female date-bearing trees by dusting them with pollens from the male date palms. By a little observation and some philosophy the Greeks and Romans added to the knowledge of sexuality in plants. Pliny, an anecdotalist of 50 B.C., and not a naturalist, wrote that pollen dust was the material of fertilization. He further stated, "naturalists claim that all trees and even herbs have the two sexes." Subsequent to this the subject received scant mention in books. It was not until 1694 that the true function and role of pollens in the reproductive process was scientifically understood. At this time, Rudolph Camerarius experimented with flowers by removing the male flowers from the vicinity of the female flowers and found that no seeds developed. From this he concludes that pollens developed in the stamens are necessary to fertilize ovules for production of seeds.
The closing chapters on experimentation with pollens are yet to be written. With the rise of hay fever, there came a renewed and increased intensity in the field of pollen research. Entire books have been devoted to the subject of pollens only. Innumerable laboratory, field, and clinical investigators have labored to obtain answers to the questions on pollens. The list of names includes ancient, early, and modern naturalists, botanists, chemists and doctors, such as: Theophrastus, Herodotus, Pliny, Alpino, Milling-tort, Grew, Malpighi, Camerarius, Logan, Kolreuter, Sprengel, Purkinje, Von Mohl, Blackley, Dunbar, Scheppegrell, Durham, Koessler, Planta, Duke, Heyl,Pope, Wodehouse, Thomen, Coca, Stull, Sherman, Bernton, Love-less and literally hundreds of others, too numerous to mention here. We shall describe in detail the work of some of these men in our historical and biographical chapter. We make mention of these men to give credit to their highly scientific papers and books from which we have gathered the answers to the questions on pollens and their significance in the hay fever picture.
The pollens responsible for hay fever are yellow-colored, light-weight, dry, and powdery in appearance. In size they vary from 1/l00 of an inch to 1/10,000 of an inch in diameter. Obviously they are not easily seen without the aid of a microscope. However, we are speaking of individual pollen grains. Pollens as you see them on plants are usually in clumps. If you rub your fingers across a pollinating ragweed plant you are likely to gather several thousand pollen grains at once. As viewed by the naked eye, pollen grains of different plants look alike, but under: the microscope they are seen to have a variety of shapes and structures. These shapes have been described as being similar to minute footfalls, golf balls, soccer balls, deflated volley balls, water wings, spiculated or spiny spheres and ellipsoids.
In structure, pollen grains are shown to have many distinguishing characteristics. Minute examinations indicate that pollen grains from different classes of plants differ in appearance. Descriptions show that pollen grains of the same species and of closely related species tend to be alike. That is to say, grass pollens can be easily distinguished from ragweed pollens but pollens from different types of ragweed plants have the same characteristics except for differences in size.
Pollen grains like human sperms are living things. They have group characteristics due to heredity, birth marks, and developmental scars. The identifying structures of pollens consist of their type of outer coat, the shape of their germ pore through which the pollen tube later emerges, a series of furrows that differ in shape and number, and a symmetrical pattern of overall sculpture. By such markings, experienced laboratory botanists are able to recognize the pollen grains and know to what family group they belong. This knowledge, as you shall see, has proved immensely valuable in the study of many phases of the hay fever problem.
COLLECTING AND OBSERVING POLLEN BEHAVIOR
Gathering samples of pollen from the air has been used for a great many purposes. From the atmospheric samples, pollens responsible for hay fever are identified and the degree of concentration in any area calculated. From such atmospheric studies, Durham has prepared charts evaluating some of the hay fever resorts in North America. Other investigators have published information giving the kinds of pollens and periods of greatest concentration for particular localities. Such information is needed by doctors and may be used to good advantage in handling the hay fever cases in their community.
With the aid of boats and airplanes, pollen concentrations have been noted 30 miles out to sea and 1700 feet up in the air. Pollens have been observed to be swept by winds many hundreds of miles from their place of origin. The significance of this floating or traveling ability of pollens will be reviewed in the discussion on hay fever in cities and the problem of increasing prevalence of hay fever.
The study of pollen concentrations in the air under a variety of conditions has helped to explain the relation-ship between hay fever and such phenomena as wind, rain, humidity, temperature, altitude, and the effect of day or night on the severity of your symptoms.
The methods for conducting the studies of pollen concentration are rather simple. They have not varied to any great extent from the time Blackley first sent up kites containing glass slides, to the present practice of exposing slides from airplanes. The technique consists of ex-posing to the atmosphere rectangles of glass which are ordinarily used as microscope slides. The glass plates are covered with a thin film of vaseline and placed in a flat position at various levels and areas to be studied. Slides have been placed atop 20 foot buildings, 100 foot buildings, i000 foot structures and on New York skyscrapers. They may be exposed on window ledges to study certain directional winds, or at weather observatory towers. The slides are protected against rain and large particles by a cover placed 10 inches above the slide. The slide is examined under the microscope and the pollens identified by experienced technicians. The number of pollen grains in a unit area of one and four fifths square centimeters is counted. This figure is multiplied by a constant and reported as "concentration of pollens per cubic yard of air."
DIGGING FOR POLLENS
A somewhat different type of pollen collection consists of digging deep down into the earth for them. This is done by men who may be described as geological botanists or botanical geologists, as you wish. Technically they are known as paleobotanists. Their purpose is to obtain fossils of pollen grains buried thousands of years in peat and sediment. The depth and nature of the soil deposits, from which the pollen fossils are obtained, coupled with a knowledge of the types of pollens, enables these experts to trace the"recent" history of the forests as they existed thirty to fifty thousand years ago. Pollen grains lately, obtained from oil shales in Colorado and Wyoming have given a picture of the flowers and trees in these regions 40 million years ago. Perfectly preserved pollen covers have been found in coal measures calculated to have been shed 250 million years ago during the carboniferous age. These discoveries indicate the almost imperishable nature of the outside covers of the pollen grains.
LASTING POWER OF POLLENS
If pollen grains can retain their external appearance for millions of years, you may well ask, "How long can they live?" And if you are interested in pollens be-cause of hay fever, you probably wish to ask, "How long can pollens cause their irritation to the hay fever sufferer?"
In an effort to answer these questions pollens of many types have been subjected to a variety of experimental conditions. The results of these experiments show that under conditions of dry atmosphere and low temperature pollens can live or retain their fertilizing ability for a maximum extent of time. The periods of time differ for the various pollens, ranging from one day to a little less than a year. However, it has been well established that the ability of pollens to produce hay fever symptoms is in no way related to its fertilizing power or length of life as it may be called. Moreover, much to the sorrow of sufferers, hay fever pollens, if kept dry, can retain their ability to produce unpleasant effects for decades. If dampened, the lasting effects of their harshness is immeasurably reduced.
Laboratory experiments to test the irritating power of pollens under varying circumstances have given us much information about the relation between hay fever and climatic conditions. Clinical or practical experiments to test how long pollens can be kept and still produce symptoms have been tried by many doctors. Dr. August Thomen cites an instance in which he tested the effects on several hay fever patients, of ragweed pollens preserved in a private herbarium from 1887 to 1927. He found these pollens,after forty years, to be practically as active as fresh pollens.
POLLENS FOR THE LABORATORY
In order to study pollens in the laboratory rather interesting techniques of collecting them on a wholesale basis have been developed. To classify and describe the pollen grains they have to be gathered directly from the plants under controlled conditions. This is done by two rather simple methods. One consists of cutting off the flowering stems and placing them in pans of water with the flower tips leaning out over the edge of the pans. Sheets of glazed paper are placed under the overhanging edges to catch the pollens when the flowers are tapped the following clay. A second method consists of tying paper bags over the blossoms in the field at the time they start to pollinate. The bags are later removed and the pollen emptied out. These methods are similarly used in collecting pollens for commercial use. The pollens related to hay fever are needed by drug manufacturers in preparing pollen ex-tracts for hay fever diagnosis and treatment. Pollen collecting has thus become a profitable occupation for a great many individuals.
IS THERE POISON IN POLLENS
Laboratory work on pollens, of an entirely different nature, has been that of chemical analysis. After you learn that pollens are the cause of your hay fever, it is only natural for you to ask, "What is there in these pollens that makes them do what they do? Is it a poison? Do non-hay fever pollens contain the same substances?" For the purpose of answering these questions chemists have made de-tailed analyses of pollens. To which purpose is always added the unspoken thought that the answers will give a clue to the cure or prevention of hay fever.
The results of chemical explorations showed hay fever pollens to contain more than twenty-five well defined substances. The major content of these pollens consists of proteins, fats, carbohydrates, sugars, enzymes, and water. There are shown to be small percentages of lecithin, alcohol, ash, and other minerals. An exhaustive chemical analysis of ragweed pollens was made by F. Heyl, who wrote six papers on the subject. On the basis of his work, he concludes that except for coloring substances and possibly protease, none of the 27 substances found in ragweed pollens shows a chemical specialization different from other cells. From these and other chemical experiments with pollens, the conclusion reached is that at present there are no manifest chemical differences between hay fever producing pollens and those which do not cause hay fever. But the active substance in pollens responsible for hay fever symptoms is either a protein or some substance closely associated with proteins.
If the conclusion reached is true, it follows that hay fever pollens do not contain a chemical which is poisonous as-such. However, it has been shown that of the pollens which do cause hay fever some seem to cause greater reactions than others. Thus in an individual allergic to both grass and ragweed the latter generally causes more numerous and intense symptoms. The difference in irritating effects has been referred to as the degree of toxicity of the pollen. The word toxicity is here misleading for it implies a presence of poison. A preferable description of the relative irritating effect of pollens might be degree of "reactive intensity."
The point of view endorsed by most authorities is that, whatever substance is responsible for producing hay fever symptoms, it is formed within the body of the sensitive person. This of course fits in with the fact that if an individual is not allergic to pollens he may sniff billions of them with never any effects, as is indeed the case with many laboratory and field botanists.