578 



NA TURE 



[April 19, 1906 



migration from the northern flora. It must, how- 

 ever, be borne in mind that lycopodiaceous plants 

 existed in the far south in the Lower Carboniferous 

 epoch. 



Another characteristic member of the northern flora, 

 which is not included in lists of plants from Gond- 

 wana Land (the name given by Suess to the southern 

 continent which supported the Glossopteris flora), is 

 Cordaites. It is, however, probable that the strap- 

 like linear leaves known as Noeggerathiopsis, which 

 are abundant in the southern Palaeozoic province, are 

 in some cases at least generically identical with 

 Cordaites. This opinion, previously expressed by the 

 reviewer, was strengthened by an inspection of some 

 leaves recently discovered by Mr. Leslie which he 

 had an opportunity of seeing last summer at 

 Vereeniging. We have as yet no satisfactory evidence 

 that the Cycadophyta were represented in the true 

 Glossopteris flora. Similarly, we cannot assert with 

 confidence that the few specimens compared bv 

 various writers with the existing Ginkgo biloba 

 afford any proof of the existence of the ginkgoales. 

 The coniferales did not play a conspicuous part in 

 the southern vegetation ; various fragments have been 

 referred to Voltzia and other genera, but such speci- 

 mens as occur appear to be indistinguishable from 

 northern Triassic and Rhastic forms. 



Although recent work has perhaps tended to bring i 

 more closely together the northern and southern 

 Permo-Carboniferous floras, there can be no doubt 

 as to the correctness of the view that the later 

 Palaeozoic vegetation of India, South America, South 

 Africa, and Australia differed sufficiently from that 

 of the northern hemisphere to justify the recognition 

 of two botanical provinces. The southern flora lacks 

 the richness and variety which characterise the 

 northern ; the number of genera is smaller, and in 

 many localities the abundance of Glossopteris — almost 

 to the exclusion of other genera — suggests a greater 

 monotony in the vegetation. To some extent the 

 apparently greater wealth of the northern flora may 

 be the result of exceptionally favourable conditions 

 for the preservation of land plants, but this does not 

 account for the strikingly different facies. The exist- 

 ence of widespread Glacial deposits in India, South 

 Africa, and Australia furnishes us with a probable 

 means of explaining the uniformity in the vegetation 

 of Gondwana Land and the contrast which it presents 

 to that of the northern hemisphere. In the case of 

 many European genera we are able to make use of 

 anatomical characters as an index of conditions of 

 growth, but the almost complete absence of petrified 

 specimens in the southern province compels the 

 admission that we cannot claim to recognise in the 

 plants themselves any satisfactory evidence as to the 

 nature of the climate in which they grew. 



We can cordially recommend Mr. Arber's volume 

 as the best and most comprehensive account of the 

 Glossopteris flora which has been written ; he has 

 produced a book bearing the impress of wide know- 

 ledge and of a well balanced critical faculty, which 

 cannot fail to be of the greatest value to both 

 geologists and botanists. A. C. Seward. 



NO. I903, VOL. 73] 



A GROUP OF TEXT-bOOKS OF PHYSICS. 



(1) The Organised Science Series: (i) First Stage 

 Physiography (Section I.). Edited by Dr. R. W. 

 Stewart. Pp. xiii + 256; diagrams. (London: 

 University Tutorial Press, Ltd., 1905.) Price 2s. 



(2) Science Handbooks for Laboratory and Class- 

 room : Elementary Physics (Third Year). By John 

 N. Brown. Pp. 1 1 1 + diagrams. (London: Blackie 

 and Son, Ltd., 1905.) Price 2s. 



(3) Examples in Physics. By C. E. Jackson. 

 Pp. vi+172. (London: Methuen and Co., n.d.) 

 Price 2s. 6d. 



(4) Advanced Examples in Physics. By A. O. Allen. 

 Pp. 60. (London: Edward Arnold, n.d.) Price 

 is. 6d. 



(5) Physics. By Charles R, Mann and ( ieorge R. 

 Twiss. Pp. x + 453; illustrated. (Chicago: Scott, 

 Foresman and Co., 1905.) Price 1.25 dollars. 



T'HE stream of physics text-books continues to 

 flow. The large number of institutions in 

 which this subject is now taught probably makes in- 

 evitable a corresponding multiplicity in the text-books 

 issued. Each teacher or group of teachers finds some- 

 thing lacking in the books available for his classes, 

 and at the first opportunity a new manual is produced. 

 But besides the stimulus of this thoroughly healthy 

 quest of the ideal, the requirements of examination 

 syllabuses are important factors in giving rise to 

 publication. Each examination has its independent 

 syllabus somewhat arbitrarily selected from the sug- 

 gestions of the members of a board, meeting in com- 

 mittee, and the result is that every examination is 

 thought to require a special text-book by those who 

 wish to secure a maximum of passes for their pupils 

 al the least expenditure of labour. 



(1) Although the latter motive is distinctly present in 

 connection with the first of the books in our list, we 

 must at the same time readily admit that it is a 

 most admirable volume except in name. It is a 

 mystery why one part of chemistry added to two parts 

 of physics should produce " physiography." but of 

 course Dr. Stewart is not responsible fur this. The 

 book has been written to meet the requirements of 

 the Board of Education in regard to the examination 

 bearing its name. Dr. Stewart is no novice in the 

 writing of text-books. He is alive to the difficulties 

 which pupils encounter, and he removes them in 

 advance. The outcome is a manual which rises far 

 above the particular purpose for which it was written, 

 and it may be confidently recommended as a very 

 satisfactory introduction to physics and chemistry suit- 

 able for school use. It contains a large number of 

 examples, many of which are worked out. 



(2) Mr. Brown's handbook on elementary physics 

 forms one of a series issued under the general editor- 

 ship of Dr. J. G. Kerr. It is intended as a third 

 year's school course, practical and theoretical. The 

 mailer is to some extent of the same kind as the 

 physical part of Dr. Stewart's text-book; we cannot, 

 however, bestow the same praise upon it. The 

 theoretical part is very meagre, and, moreover, in 



