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THE publication of a short but comprehensive A text-book of palaeobotany in English is a noteworthy event, for great progress has been made during the last forty years in our knowledge of fossil plants, and the discoveries of the latter half of this period must eventually revolutionize many widely accepted views on evolutionary morphology. The author, who is a member of the staff of Harvard, has all the enthusiasm of youth, and has produced a book which covers a very wide field of study. The subject is treated mainly from a phylogenetic point of view, the historical evidence relating to each of the main groups of plants being considered. A few chapters are devoted to a review of the floras of the great geological epochs and to more general topics. Each chapter is accompanied by a bibliography of the more important papers, mainly from recent publications. There is a large number of illustrations which add to the interest and value of the book. Many of them are reproductions of photographs of actual specimens, though these vary in quality. Textbook of Paleobotany By William C. Darrah. (Century Biological Series.) Pp. xii + 441. (New York and London: D. Appleton-Century Co., Inc., 1939.) 20s. net.

DURING the last twenty years great progress has been made in the study of coal. Instead of treating it only as a material which on combustion gave certain products, investigators have been studying the material itself, its constituents, their mode of occurrence and association, and their probable method of origin. Coal is a rock rather than a mineral, and much of the progress that has been made has come from its examination by petro-logical methods. These methods have been developed independently in England, America, and Germany, and their results have been described in many widely scattered publications, consequently a brief summary of the work with a full list of references is very valuable. Kohlenpetrographisches Praktikum. Von Dr. Erich Stach. (Sammlung naturwissenschaftlicher Praktika, Band 14.) Pp. iv + 196. (Berlin: Gebruder Borntraeger, 1928.) 10.80 gold marks.

WE regret to record the death of Sir Albert Seward on April 11 at the age of seventy-seven. Albert Charles Seward achieved outstanding success as an investigator, a teacher, a writer and an administrator. Most of his life was spent in Cambridge, where the University and two of its colleges owe much to his untiring energy, but his work also extended over a much wider field and few scientific men have been so widely known and so universally popular.

THE considerations put forward by Dr. Delbruck and Dr. Timofeeff-Ressovsky are of undoubted importance and were in my mind when my lecture was written. In fact, my suggestions were based on the parallelisms between induced variation and the so-called spontaneous mutations, together with the quantitative relation mentioned in Section 1 of their letter. But I consider that at present the view that ” spontaneous mutation can be explained without an admission of special mutation-inducing agents in the external environment” is an assumption which has yet to be proved. The fact that more spontaneous mutations occur than would be expected to result from natural radiation is not a final objection. For as Prof. Blackett pointed out1 there are certain differences between the nature of the ionisation produced by cosmic rays and by gamma rays, so that it cannot be concluded that the effects of both, when of the same average intensity, are always identical. The differences are connected with the production of bursts and showers. We know that these occur at sea-level2 and in water3 while their frequency increases with altitude4 more rapidly than the cosmic ray ionisation. Thus we are yet scarcely in a position to calculate the mutation rate due to cosmic rays from the X-ray data. Again, some plant species appear morphologically stable over long periods of time, while others are unstable. Apparently X-radiation may set up conditions causing unexpected variation in more than one successive generation of plants5, and I think we may have to distinguish between the manifestation of genetic instability and its original cause.

The Natural Philosophy of Plant Form By Dr. Agnes Arber. Pp. xiv + 247. (Cambridge: At the University Press, 1950.) 25s. net.

PALAEOBOTANISTS in many countries heard with regret the news of the sudden death of Birbal Sahni on April 10. Hip slight figure, his modest personality and polished manners were well known at international gatherings of botanists and geologists ; few Indian men of science can have been more widely respected. He was not only a diligent research worker but also a stimulating teacher and a good organiser. He did much to develop his own subject and the cause of natural science in India.

Literature and Science By B. Ifor Evans. Pp. 114. (London: George Allen and Unwin, Ltd., 1954.) 8s. 6d. net.