1^,6 



NATURE 



[November 30, 1911 



there is evidence of extensive desiccation in western 

 North America, southern South America, north-central 

 Africa, and central Australia; and physical changes 

 which arc not yet understood led to a glacial epoch 

 in the northern hemisphere in Pleistocene times. These 

 phenomena had doubtless much to do with the ex- 

 tinction of the large quadrupeds and the impoverish- 

 ment of the mammal fauna. Civilised man has con- 

 tinued the destruction. 



The whole of this fascinating story is told in detail 

 by Prof. Osborn, who not only discusses the mammals 

 themselves, but also describes the rocks in which 

 their remains occur, and briefly notices the successive 

 changes in geography which they indicate. His work 

 is illustrated by numerous text-figures of skeletons, 

 restored sketches of extinct mammals made by the 

 American Museum of Natural History, photographs 

 of scenery, and diagrammatic geological sections. As 

 might be supposed, much of it is extremely technical, 

 and to be used for reference rather than systematic 

 reading ; but it is enlivened throughout by a succession 

 of interesting generalisations, which are all the more 

 valuable as having been either suggested or confirmed 

 by the author's own researches. The peculiar feature 

 of Prof. Osborn's book, indeed, is its stimulating 

 freshness, and he is to be congratulated on the impulse 

 which it is certain to give to the studies with which 

 it deals. A. S. W. 



GEOGRAPHICAL DISTRIBUTION OF FERNS. 

 Die Geographic der Fame. By H. Christ (Basel) 



Pp- 357 + 3 maps. (Jena: Gustav Fischer, 1910.) 



Price 12 marks. 



DR. CHRIST has produced a volume of remark- 

 able interest on the geographical distribution 

 of ferns, which forms a worthy companion to 

 Schimper's well-known " Pflanzen-Geographie auf 

 physiologischen Grundlage." The book has been 

 arranged in a somewhat similar manner to Schimper's 

 "Plant Geography," and is divided into two parts. 

 The first consists of 136 pages, devoted to considera- 

 tions of the effects of soil, climate, &c., on the distri- 

 bution of ferns, and in the second part the ferns of 

 the different geographical areas are described in detail. 



To the general botanist, and more particularly to 

 the ecologist, the first portion of the book has the 

 greater interest. Ferns, unlike the flowering plants, 

 though very widely distributed, are not universally 

 found over the surface of the earth, since they are 

 definitely limited as to their environment by the need 

 for water, and though many species are remarkable 

 for their capability of resisting desiccation, yet they 

 are unable to grow where the rainfall is below a 

 certain amount. Being in the main shade plants, 

 their maximum distribution tends to follow the wooded 

 areas of the globe ; and the dry desert areas are almost 

 destitute of ferns. 



Though mainly found growing on humus, some 

 ferns are affected by the nature of the substratum, and 

 this is especially the case with calcareous soils. It 

 may often happen, however, that chalk-shunning 

 ferns may be found on that formation owing to the 

 NO. 2196, VOL. 88] 



I is overJ| 



depth of humus by which the calcareous soil is ov« 

 laid. 



Striking examples of ferns which avoid the chalk 

 are afforded by Asplenium septentrionale and by »V" 

 world-wide Pteridium aquilinum — the bracken fen 

 which is found in both hemispheres, from "the equa 

 to the poles." Asplenium viride and Cystopteris t»? 

 tana, on the other hand, may be cited as examples ot 

 species characteristic of the chalk. Halophytes, again» 

 have their fern representatives, and Acrostichum 

 lomarioides from the brackish swamps of tropicat 

 America, and A. auretim, which grows in the Rhizo» 

 phora estuaries, are striking examples of this type of 

 plant. 



Then again there are the fresh-water swamp ferns, 

 such as the widely distributed Dryopteris thelypteris 

 and the well-known water fern, Ceratopteris thalic' 

 trioides. 



The majority of ferns are perennial, but there are 

 a few exceptions, of which Ceratopteris is one, and 

 also the annual fern, Anogramma leptophylla. 



Ferns afford parallels to Phanerogams in their 

 choice of habitats and relations to climatic con- 

 ditions, and also in their external forms they provide 

 counterparts to other types of vegetation. We fin<| 

 them, for example, as epiphytes; tree ferns; 

 scramblers or bramble ferns (Gleichenia, Odontosoria, 

 &c.) ; twining ferns, such as Blechtium volubile; tendri 

 climbers {Lathyropteris madagascariensis), and creep 

 ing epiphytes or rhizome climbers, which are wd 

 illustrated by the aroid-like Oleandra neeriformis. 



The general biological features of hygrophytic femSj 

 hairs, secretions, storage organs, &c., are alsd 

 described with a wealth of illustration. 



An interesting section is devoted to the description 

 of the xerophytic types, many of which have thdl 

 home in the Andes, on the same lines as that for thl 

 hygrophytes. Two characteristic forms may hi 

 recognised : the Cheilanthes t}'pe, with short rhizome, 

 deep roots, and small hairy pinnae, and the Elapho 

 glossum type, where the rhizome is thick and creepinj 

 and the leaves tongue-like, leathery, and simple. The 

 genera Cyclophorus, from the Old World, and Elapho- 

 glossum, centred in the Andes, afford the most strik- 

 ing examples. 



Ferns of high alpine or arctic regions are few, a 

 as compared with the phanerogamic vegetation 

 such situations, are not particularly characteri? 

 Cryptogramma and Woodsia, however, maybecitcc: 

 typically northern alpine forms, while PolysticJi 

 mohrioides is a typical antarctic-andine species. O: • 

 of the highest know-n species is another Polystichum. 

 P. Duthci, from Kumaon, which occurs at an altitude 

 of from 13,000 to 17,000 feet. 



The bulk of the second part of the book is concern 

 with the fern flora of the different geographical 

 gions, but it is preceded by some very interest! 

 pages dealing with general questions of geographic 

 distribution, such as the effect of the Ice age and the 

 relics of the fern ftora of past ages. The distribution 

 of several genera is outlined, but space does nol 

 permit of a review of this section of the book in 

 further detail. Attention may, however, be directed 

 to the remarkable case of distribution afforded bv 



