1

The advent of these plants in the flora of this period, according to existing fossils, appears somewhat sudden, so much so that palaeobotanists have been disposed to think that this epoch indicates the existence of a mutative period in plant life. In fact, that during the time the chalk rocks were forming that plants suddenly all over the world produced species differing essentially from those which had preceded them. It is necessary, however, to take into consideration the existence of a group of fossil plants known as Cycads, which were probably derived from a common stock and "which are are in close connection with the ancestors of modern flowering plants; thus flowering plants can be linked on to the series that runs through the Cycads directly to the primitive ferns." It is only within the last few years that the important extinct group of plants-Pteridosperms-has been recognized. Nevertheless, they form the most numerous plants of the Carboniferous period and have displaced the ferns from the position they were hitherto supposed to hold as the dominant plants of the coal measures. Facts such as these render us cautious in accepting the idea that the flowerless flora of the ancient world became suddenly changed during the Cretaceous epoch into flowering plants. It is clear that the vascular and reproductive organs of the plants of ancient geological periods, as they grew taller and came to inhabit a dry soil, must, under the laws of natural selection, have undergone certain modifications. From the microscopical examination of the tissues forming these primitive plants we find that alterations in their structure have gradually taken place, culminating in the appearance of the flowering plants of the Cretaceous epoch.

Dr. M. C. Stopes in the concluding chapter of his excellent work on "Ancient Plants" (p. 178) states that "the group of fossil plants do not now appear isolated by great unbridged gaps, as they did even 20 years ago;" by means of the fossils either direct connections or probable links are discovered which connect series and families. We may add that plants now growing in the Nile Valley are similar in character to those represented on the monuments of the earliest Egyptian dynasties. In the stable climate and conditions of the Nile Valley these plants for thousands of years have retained their character; but if removed to a different soil and climate such as that of England, in the course of a few generations they become variable and thus undergo marked modifications. We hold this result to be attributable to the response of their living protoplasm to the action of changes of environment, which in the course of time we believe, under the influence of natural selection, might possibly lead to the production of new varieties, if not actual species. The following details concerning a remarkable series of variations in certain Fox

1 Ancient Plants, by M. C. Stopes, p. 103.

glove plants appear to afford us reliable evidence in favor of the idea, that under certain unknown conditions the flowers of a wild plant may become suddenly and completely altered in character, and that variations of this description are passed on from one to succeeding generations by means of the germ cells.1

From a packet of Fox-glove seeds (Digitalis purpurea) sown in the year 1906, 54 plants were, in June, 1907, planted in a shrubbery of fir trees with an undergrowth of laurels. Of these plants, 51 grew into normal Fox-gloves, but the 3 remaining plants were sports, which we may distinguish by the letters A, B, and C.

A. In this plant the flowers of the lower half of the stem possessed only a bifid upper petal and seven stamens united at their bases. The flowers of the upper part of the spike were normal.

B. A fine, well-grown plant 4 feet high; throughout the whole length of the spike the flowers consisted of a bifid upper petal, seven stamens, and style. The upper part of this spike was isolated; it produced abundant self-fertilized seed.

C. The spike of this plant grew to be 5 feet high; from base to apex its flowers consisted of nine stamens and a style, with no vestige of petals.

It is unnecessary to follow the history of plant A, as it was only the lower part of the spike in which the flowers were abnormal, and the stem was not isolated.

Seed taken from the upper covered part of the plant B, whose flowers consisted of a bifid petal, 7 stamens, and a style, germinated abundantly; 21 of these plants flowered in 1909. Thirteen of these 21 plants produced spikes of the parent type, and 8 of the 21 plants produced normal Fox-glove flowers. One of the 13 plants grew to be 5 feet 1 inch high, its spike producing 1 bifid petal and a style; but its terminal flower consisted of 22 stamens and a large flask-shaped carpel (divided into 7 compartments) and style, but having no corolla; that is, it had no petals. (As shown in photograph exhibited.)

The season of 1909 was sunless, with constant rain; consequently, all covered plants suffered much from mildew, but I managed to collect some self-fertilized seed from the terminal flower of the plant referred to, and this seed germinated and flowered in 1911. Every one of the 12 plants I reared from the seed of the terminal flower produced flowers precisely like the parent. Two of these plants were isolated and their self-fertilized seed germinated freely (September, 1911).

The seed originally collected from the covered part of plant C of 1907 had produced plants which, in 1909, gave flowers precisely

1 N. C. Macnamara, on Mutations in Fox-glove Plants. Linnean Society of London, General Meeting Nov. 16, 1911.

similar to the parent plant. Self-fertilized seed from these plants (1909) in 1911 produced plants exactly like those of 1907-i. e., flowers having nine stamens and a style, but no petals. Self-fertilized seed from these plants are now (September, 1911) germinating freely. Some of the plants, however, of 1909, in place of a tall single spike, grew some seven or eight shorter spikes, each flower of which had nine stamens but no petals.

It seems that a certain number of the Fox-glove seeds sown in the year 1906 contained elements in a condition such as that described by De Vries as being "impressed by an impulsive mutability," for some of the flowers produced by these seeds were sports. Seeds from these sports produced their like in 1909; and, further, these latter plants bore some terminal flowers totally different in character from the parent sport from which they were derived. Seeds from these terminal flowers produced their like in the year 1911, so that I have now two different strains of Fox-glove plants derived from the seed sown in 1906, and these strains have resulted from self-fertilized flowers-that is, from flowers carefully protected from insects or other means of cross fertilization. It is, however, doubtful if these varieties would have been maintained in a state of nature. While specific stability under constant conditions appears to be the rule in nature, it is widely different in cultivation. When a plant is brought under cultural conditions it maintains its type for some time unaltered, then gives way and becomes practically plastic. It is certain, therefore, that before we can accept De Vries's hypothesis of the origin of species by mutation we must have further and more conclusive evidence on the subject than that which is now available. On the other hand, Huxley's conclusion regarding the Darwinian hypothesis still holds good. He states that all species have been produced by the development of varieties from common stocks; the conversion of these, first into permanent races, and then into new species, by the process of natural selection, which process is essentially identical with that of artificial selection by which man has originated the races of domestic animals, the struggle for existence taking the place of man; and exerting, in the case of natural selection, that selective action which he performs in artificial selection.

The evidence brought forward by Darwin in support of his theory is of three kinds. First, he endeavors to prove that species may be originated by selection; secondly, he attempts to show that natural causes are competent to exert selection; and, thirdly, he tries to prove that the most remarkable and apparently anomalous phenomena exhibited by the distribution, development, and mutual

1 Nature, Nov. 28, 1907.

relations of species can be shown to be deducible from the general doctrine of their origin which he propounds, combined with the known facts of geological change; and that, even if not all these phenomena are at present explicable by it, none are necessarily inconsistent with it; on the other hand, since Huxley's time Darwin's theory has been strengthened by many new facts.'

1 Huxley's Essays. Everyman's Library, p. 331. See also The International Scientific Series, vols. 95 and 97. Kegan Paul. London, 1908 and 1910.

MAGNALIA NATURÆ: OR THE GREATER PROBLEMS OF

BIOLOGY.

By D'ARCY WENTWORTH THOMPSON, C. B.,

Professor of Natural History in University College, Dundee (University of St. Andrews).

The science of zoology, all the more the incorporate science of biology, is no simple affair, and from its earliest beginnings it has been a great and complex and many-sided thing. We can scarce get a broader view of it than from Aristotle, for no man has ever looked upon our science with a more farseeing and comprehending eye. Aristotle was all things that we mean by "naturalist" or "biologist." He was a student of the ways and doings of beast and bird and creeping thing; he was morphologist and embryologist; he had the keenest insight into physiological problems, though his age lacked that knowledge of the physical sciences without which physiology can go but a little way; he was the first and is the greatest of psychologists; and in the light of his genius biology merged in a great philosophy.

I do not for a moment suppose that the vast multitude of facts which Aristotle records were all, or even mostly, the fruit of his own. immediate and independent observation. Before him were the Hippocratic and other schools of physicians and anatomists. Before him there were nameless and forgotten Fabres, Rosels, Réaumurs, and Hubers, who observed the habits, the diet, and the habitations. of the sand wasp or the mason bee; who traced out the little lives and discerned the vocal organs of grasshopper and cicada; and who, together with generations of bee-keeping peasants, gathered up the lore and wisdom of the bee. There were fishermen skilled in all the cunning of their craft, who discussed the wanderings of tunny and mackerel, swordfish or anchovy; who argued over the ages, the breeding places, and the food of this fish or that; who knew how the smooth dogfish breeds, two thousand years before Johannes Müller; who saw how the male pipefish carries its young, before Cavolini; and who had found the nest of the nest-building rockfishes before

1 Presidential address delivered to the zoological section of the British Association Aug. 31, 1911. Reprinted by permission from author's printed copy.