172 



NATURE 



[August 10, 191 1 



Chapter ii. is devoted to the Bennettitales, the char- 

 acteristic Mesozoic Cycadophytes, remarkable for 

 their anticipation of the angiospermous flower. 



The authors have been misled by the synonymy in 

 one instance, for they describe Williamsonia angus- 

 tifolia and Wielandiella as distinct plants, whereas 

 they are merely two names for the same thing (pp. 66 

 and 86). A more serious error is the statement that 

 Nathorst confirms the view that the flowers of the 

 Yorkshire Williamsonias are bisporangiate strobili 

 (p. 76). Nathorst's conclusion is that these flowers 

 were monosporangiate (unisexual). 



The derivation of the Mesozoic Bennettitales from 

 the Palaeozoic Cycadofilicales will be generally 

 accepted, but the statement that " the bisporangiate 

 character of the strobilus is probablv to be explained 

 by the bisporangiate character of the fronds of those 

 Cycadofilicales which gave rise to Bennettitales " 

 (p. 87) is more open to question. We have at pre- 

 sent no evidence of the existence of bisporangiate 

 fronds in the Palaeozoic group ; neither is it necessary 

 to assume their existence in order to explain the 

 association of stamens and carpels in the same flower. 



Chapter in., on the Cycadales, is no doubt the best 

 account we have of this important and fascinating 

 family. A large number of original observations, by 

 members of the Chicago School of Research, are 

 embodied, and there are some very fine new figures. 



Dioon edule, a Mexican Cycad, said to attain an 

 age of 1000 years, has now been added to the list of 

 species in which fertilisation by motile spermatozoids 

 has been observed. 



The statement that the Cycadales are "probablv not 

 so old as either the Ginkgoales or the Coniferales " 

 may need revision. Our records are scanty, but 

 carpels scarcely distinguishable from those of recent 

 species of Cycas are known as far back as the Lias. 



In the chapter on the Palaeozoic Cordaitales there 

 is not much room for novelty, for here our knowledge 

 has advanced but slowly of late. The current views of 

 their affinities are adopted. The related phylum of 

 the Ginkgoales (chapter v.), of which there is only 

 one survivor, the maidenhair tree, is regarded as 

 retaining certain primitive features in common with 

 the Cycadophytes, while it has advanced more in the 

 direction of the Coniferales, and has developed certain 

 peculiarities of its own (p. 217). 



Chapters vi. and vii. are on the Coniferales, which, 

 from their extent and variety, naturally demand a 

 fuller treatment than any other group. The account 

 given is excellent, and contains much of interest, but 

 one realises that the Conifer problem still remains to 

 be solved. 



The class is divided into Pinaceae and Taxaceae, 

 but it is very doubtful whether even this first group- 

 ing is natural, for the Podocarps among the Taxaceae 

 seem to have little to do with the Yews, while they 

 have much in common with the Araucarians among 

 Pinaceae. 



Perhaps too much is made of the supposed special 

 antiquity of the Abietineae (firs). The arguments in 

 support of the primitive nature of this tribe are not 

 altogether convincing. 



In stating that the Taxaceie have not been recog- 

 . J 180, VOL. 87] 



nised further back than the Cretaceous (p. 349), the 

 authors ignore Nathorst's suggestion that the Rhaetic 

 genera Stachyptaxus and Palissya may be early re- 

 presentations of the Podocarps. 



The heterogeneous group of the Gnetales forms the 

 subject of chapter viii. We think that more stress 

 might have been laid on the possible affinity, origin- 

 ally suggested by Wieland, between Welwitschia and 

 the Mesozoic Bennettitales. The hermaphrodite 

 flowers and monadelphous stamens occurring in Wel- 

 witschia are striking points of agreement with the 

 extinct group. 



The account of the three extremely diverse genera 

 which make up the Gnetales is of much interest, and 

 contains various details hitherto not readily accessible 

 to the student. The relationship of such isolated 

 types, with no known fossil historv, necessarily re- 

 mains obscure. 



The final chapter, on "Evolutionary Tendencies 

 among Gymnosperms," previously published in part 

 as a separate paper, sums up the main results. The 

 diagram on p. 409 gives a good idea of the probable 

 evolutionary connections of the various groups, though 

 in one or two points it is not quite consistent with 

 the statements in the text. Though the reviewer does 

 not agree with quite all the authors' conclusions, he 

 is in entire sympathy with their principle that 



" the relative position of any form in a scheme of 

 classification can be determined onlv by averaging all 

 its characters ; and its relative age in a scheme of 

 phylogeny can be determined only by the sure testi- 

 mony of history " (p. 425). D. H. S. 



THE EVOLUTION OF OUR ISLANDS. 



The Building of the British Isles, being a History of 

 the Construction and Geographical Evolution of the 

 British Region. By A. J. Jukes-Browne, F.R.S. 

 Third edition, rewritten and enlarged. Pp. xv + 

 470. (London : E. Stanford, 191 1.) Price 12s. net. 



THIS new edition of Mr. Jukes-Browne's well- 

 known book makes it virtually a manual of 

 the geology of the British Isles. The photographic 

 illustrations bring the relations of the rocks clearly 

 home to us, and many of them are works of art, such 

 as Prof. Reynolds's view of chalk and lavas at Gar- 

 ron Point (Fig. 61), and Mr. R. F. Gwinnell's Miocene 

 folding at Luhvorth (Fig. 63). The numerous maps, 

 suggesting the relations of land and water at various 

 epochs, suffer, as all such maps must do, from our 

 ignorance of details. The sweeping boundaries of 

 continents and the generalised forms of firths and 

 sounds are perforce unlike anything that we now 

 know upon the earth. Printed explanations on the 

 maps would greatly aid the reader, such as "area of 

 Bunter pebble-beds," "Lake-basin," and so forth. 

 There is a mysterious dotted line on Fig. m, for which 

 one must search the text, while much guidance is 

 required for the lines and colours on Fig. 57. The 

 result may, however, !"■ regarded as happy, if the 

 casual reader is sent through a lengthy chapter, to 

 find there a summary of the latest researches, and 

 evidence of a critical mind that looks eastward 

 across Europe. Mr. Jukes-Browne does not hope to 



