EARLY MICROSCOPISTS AND THE DISCOVERY OF SPORES After Lucretius, more than 1,500 years passed before men even began to be aware that the air teems with microscopic living organisms.
The discovery had to wait almost until the invention of the micro scope.
For a long time after Aristotle and Theophrastus, the lower plants lacking obvious seeds were believed to be generated spontaneously in decaying animal or vegetable matter. The same view was held of the origin of many of the lower animals. However, the minute `seeds' or spores of several kinds of plants were observed in the mass long before the invention of the microscope allowed them to be identified and observed individually. What was more natural than to suppose that these minute particles were wafted about by the winds ? The discovery of reproduction of ferns is attributed to Valerius Cordus (b. 1515, d. 1564), and spores of the fungi seem to have been observed soon after this by a Neapolitan botanist, J. B. Porta, although the rusty coloured spore deposits under bracket-fungi on beech trees must always have been familiar to the countryman.
It was P. A. Micheli (b. 1679, d. 1737), botanist to the public gardens at Florence, who first illustrated the `seeds' of many fungi, including mushrooms, cup-fungi, truffles, moulds, and slime-moulds. Further, by sowing spores on fresh-cut pieces of melon, quince, and pear, and repro ducing the parent mould for several generations, he showed that the spores of some common moulds were, indeed, `seeds' of the fungi. He noted, however, that some of his control slices also became contaminated, and he concluded that the spores of moulds are distributed through the air (see Buller, 1915).
The hand-made lenses of Anton van Lceuwenhoek rendered visible the world of minute organisms whose existence had only been guessed at before, and whose significance in nature had scarcely even been imagined. He could just see bacteria, and in his letters to the Royal Society in 1680 he described some yeasts, infusoria, and a mould. From his experiments he came to doubt the current belief in spontaneous generation; it seemed more plausible to him to suppose that his `animalcules can be carried over by the wind, along with the bits of dust floating in the air' (Dobell, 1932). The controversy over spontaneous generation was to last for a couple of centuries; but, in the second half of the eighteenth century, ideas were developed by Nehemiah Grew and E. F. Geoffrey on the function of the pollen of flowering plants. J. G. Koelreuter, in 1766, was perhaps the first to recognize the importance of wind-pollination for some plants and of insect-pollination for others. C. K. Sprengel in 1793 developed these views and concluded that flowers lacking a corolla arc usually pollinated in a mechanical fashion by wind. Such flowers have to produce large quantities of light and easily-transported pollen, much of which misses its target or is washed out of the air by rain. Thomas A. Knight in 1799 reported that wind could transport pollen to great distances.
By the beginning of the nineteenth century, therefore, it was recognized that pollen of many, but by no means all, species of flowering plants, and the microscopic spores of ferns, mosses, and fungi—as well as protozoa— were commonly liberated into the air and transported by the wind. The potential sources of the air-spora had been discovered and identified in the main before the year 1800, but their role remained obscure.