We see, therefore, that the problems which Darwin had before him in his researches into the biology of flowers were of the greatest importance, and at the same time that the point of view from which he attacked the problems was essentially a teleological one.
We may next inquire in what condition he found the biology of flowers at the time of his first researches, which were undertaken about the year 1838. In his autobiography he writes,--"During the summer of 1839, and, Ibelieve, during the previous summer, I was led to attend to the cross-fertilisation of flowers by the aid of insects, from having come to the conclusion in my speculations on the origin of species, that crossing played an important part in keeping specific forms constant." ("The Life and Letters of Charles Darwin", Vol. I. page 90, London, 1888.) In 1841 he became acquainted with Sprengel's work: his researches into the biology of flowers were thus continued for about forty years.
It is obvious that there could only be a biology of flowers after it had been demonstrated that the formation of seeds and fruit in the flower is dependent on pollination and subsequent fertilisation. This proof was supplied at the end of the seventeenth century by R.J. Camerarius (1665-1721). He showed that normally seeds and fruits are developed only when the pollen reaches the stigma. The manner in which this happens was first thoroughly investigated by J.G. Kolreuter (1733-1806 (Kolreuter, "Vorlaufige Nachricht von einigen das Geschlecht der Planzen betreffenden Versuchen und Beobachtungen", Leipzig, 1761; with three supplements, 1763-66. Also, "Mem. de l'acad. St Petersbourg", Vol. XV. 1809.)), the same observer to whom we owe the earliest experiments in hybridisation of real scientific interest. Kolreuter mentioned that pollen may be carried from one flower to another partly by wind and partly by insects. But he held the view, and that was, indeed, the natural assumption, that self-fertilisation usually occurs in a flower, in other words that the pollen of a flower reaches the stigma of the same flower. He demonstrated, however, certain cases in which cross-pollination occurs, that is in which the pollen of another flower of the same species is conveyed to the stigma. He was familiar with the phenomenon, exhibited by numerous flowers, to which Sprengel afterwards applied the term Dichogamy, expressing the fact that the anthers and stigmas of a flower often ripen at different times, a peculiarity which is now recognised as one of the commonest means of ensuring cross-pollination.
With far greater thoroughness and with astonishing power of observation C.K. Sprengel (1750-1816) investigated the conditions of pollination of flowers. Darwin was introduced by that eminent botanist Robert Brown to Sprengel's then but little appreciated work,--"Das entdeckte Geheimniss der Natur im Bau und in der Befruchtung der Blumen" (Berlin, 1793); this is by no means the least service to Botany rendered by Robert Brown.
Sprengel proceeded from a naive teleological point of view. He firmly believed "that the wise Author of nature had not created a single hair without a definite purpose." He succeeded in demonstrating a number of beautiful adaptations in flowers for ensuring pollination; but his work exercised but little influence on his contemporaries and indeed for a long time after his death. It was through Darwin that Sprengel's work first achieved a well deserved though belated fame. Even such botanists as concerned themselves with researches into the biology of flowers appear to have formerly attached much less value to Sprengel's work than it has received since Darwin's time. In illustration of this we may quote C.F.
Gartner whose name is rightly held in the highest esteem as that of one of the most eminent hybridologists. In his work "Versuche und Beobachtungen uder die Befruchtungsorgane der vollkommeneren Gewachse und uber die naturliche und kunstliche Befruchtung durch den eigenen Pollen" he also deals with flower-pollination. He recognised the action of the wind, but he believed, in spite of the fact that he both knew and quoted Kolreuter and Sprengel, that while insects assist pollination, they do so only occasionally, and he held that insects are responsible for the conveyance of pollen; thorough investigations would show "that a very small proportion of the plants included in this category require this assistance in their native habitat." (Gartner, "Versucher und Beobachtungen...", page 335, Stuttgart, 1844.) In the majority of plants self-pollination occurs.
Seeing that even investigators who had worked for several decades at fertilisation-phenomena had not advanced the biology of flowers beyond the initial stage, we cannot be surprised that other botanists followed to even a less extent the lines laid down by Kolreuter and Sprengel. This was in part the result of Sprengel's supernatural teleology and in part due to the fact that his book appeared at a time when other lines of inquiry exerted a dominating influence.
At the hands of Linnaeus systematic botany reached a vigorous development, and at the beginning of the nineteenth century the anatomy and physiology of plants grew from small beginnings to a flourishing branch of science.
Those who concerned themselves with flowers endeavoured to investigate their development and structure or the most minute phenomena connected with fertilisation and the formation of the embryo. No room was left for the extension of the biology of flowers on the lines marked out by Kolreuter and Sprengel. Darwin was the first to give new life and a deeper significance to this subject, chiefly because he took as his starting-point the above-mentioned problems, the importance of which is at once admitted by all naturalists.
