Makers of British Botany; a collection of biographies by living botanists

by Unknown

It was with the dawn of this period that Henfrey identified himself. In the 15 years of his active career (1844-1859) he devoted himself very largely to making his fellow-countrymen acquainted with the newer aspects of botany. More particularly it was the recent discoveries as to the reproduction and life history of the Vascular Cryptogams that specially engaged his interest—the researches which broadly speaking we associate with Hofmeister to-day.

Before we go on to speak of the sexuality of the Cryptogams however, a few words may be devoted to that of the flowering plants.

Sexuality of Flowering Plants. At the period when Henfrey entered on his career as a botanist no reasonable doubt remained as to the existence of sexes among the flowering plants. The theory of the sexual significance of the organs of the flower, brilliantly founded by Koelreuter in the previous century, had been perfected with a great volume of experimental proof by K. F. Gaertner the son of Joseph Gaertner of Carpologia fame.

By 1830 the mechanism of fertilisation came to light in Amici's discovery of the pollen tube which he traced from the stigma to the micropyle. The microscopic aspect of the problem was taken up with great energy by Schleiden and brought to the forefront as the burning question of the early forties. The theory of Schleiden, which applied in particular to the flowering plants, made its influence felt to such an extent in the search for evidence of sexuality among the Cryptogams, that we may conveniently state in a few words in what it consisted.

Schleiden traced the pollen tube into the micropyle, and thence to the nucellus where it depressed or invaginated the apex of the embryo-sac, and in the recess or indentation so produced the tip of the pollen tube was converted into the embryo—its actual apex being represented by the plumule. This theory was the lineal descendant in modernised trappings of the old view expressed by Morland and others at the beginning of the eighteenth century that the embryo was contained in the pollen grain, and that the ovule was no more than the brood chamber whither it must be brought to undergo further development. This erroneous interpretation of the true facts was always repudiated by Amici, and was finally overthrown by Hofmeister and Radlkofer in the early fifties. In this connection we may note in passing Henfrey's careful paper on the impregnation of Orchis Morio, published in 1856, which fully corroborated Amici. In this paper the relations of pollen tube, embryo-sac, egg-cell, suspensor and embryo were correctly interpreted, and the new point established, contrary to the assertions of previous observers, that the ovum or "germinal-vesicle," prior to fertilisation, was a naked, unwalled cell.

Sexuality in Cryptogams. By far the most important question that came to a head in Henfrey's time was that of the morphological relationships of the Cryptogams and flowering plants. Hitherto these had remained altogether obscure in the absence of reliable data based on the proper application of the microscope to the elucidation of the life histories of the lower plants. Under the influence of the Linnaean school, which had taken deep root in this country, as elsewhere, the systematic study of flowering plants had been widely pursued, and in so far as the ferns were concerned their homologies were commonly interpreted in terms of the flowering plants. Without any real guidance in fact, a great diversity of views of these homologies found expression. The following, taken from Lindley, may serve to illustrate their general nature.

The sorus was regarded as a sort of compound fruit, the sporangium as a carpel, the annulus as its midrib, and the spores as the seeds. Speculations such as these are of the same order as the crude conjectures which with less excuse relieve the answer books of examination candidates at the present time.

In the search for the male organs of the fern attention was naturally directed to the neighbourhood of the sorus, and the stomata, indusia and glandular appendages were in turn mistaken by various observers for the anthers. The "limit" was reached by Griffith who, as is stated at [page 190], conjectured that the Anabena filaments which accompany the megasporangia of Azolla were no other than the male organs of that plant.

Schleiden spoke of these researches with the utmost scorn. "For my part I am surprised that no one has yet insisted upon the presence of the organs of sense, as eyes and ears in plants, since they are possessed by animals. Such an assumption would not be a bit more absurd than the mania of insisting upon having anthers in the Cryptogams, simply because they are found in the Phanerogams."