748 



SCIENCE. 



[N. S. Vol. IX. No. 230. 



ness and in manner of presentation of this por- 

 tion, the book is probably without an equal. 

 With respect to water content as a factor, 

 Schimper's divisions agree with those of Warm- 

 ing, except that he uses the term tropophyte 

 for mesophyte to apply to all plants not hydro- 

 phytes or xerophytes. The same criticism ap- 

 plies here that has been made elsewhere against 

 Warming's mesophytes. The term is a con- 

 venient one, but it designates an ill-defined 

 group and is almost impossible in application. 

 The analysis of the conditions producing xero- 

 phytes is critical ; such conditions are here 

 grouped with reference to decrease of absorp- 

 tion and increase of transpiration. Under the 

 former are ranged small water content, abun- 

 dance of salts or humic acid in the soil, low soil 

 temperature ; under the latter, low degrees of 

 humidity of the air, high temperature, low at- 

 mospheric pressure, intense illumination. Cor- 

 responding to these characteristics, xerophytic 

 habitats are : (1) deserts and steppes, with a 

 dry substratum and a dry atmosphere, often, 

 also, with excessive heat and intense sunlight ; 

 (2) rocks and tree trunks, with low water con- 

 tent due to rapid drying ; (3) sandhills, rubble, 

 talus, with extremely porous soil ; (4) seashore, 

 solfatara, with abundant salts in solution in the 

 soil ; (5) moors, with humic acid in the soil ; (6) 

 polar areas, either in glaciated mountain ranges 

 orin arctic latitudes, with extremely low ground 

 temperature ; (7) alpine mountains with rarefac- 

 tion of the atmosphere and strong insolation. 

 The consideration of hydrophytes and tropo- 

 phytesis naturally much more restricted. Schim- 

 per regards water plants proper as descended 

 from primitive unstable amphibious forms — a 

 conclusion rather too theoretical to be gener- 

 ally accepted. He closes this section with a 

 condensed statement of the relation of water to 

 reproduction and to dissemination. 



In the consideration of temperature the 

 author expressly states that he regards this 

 factor of primary importance. He places its 

 treatment after that of water solely because the 

 modifications due to the latter are more easily 

 investigated and determined. The considera- 

 tion of temperature extremes is followed by that 

 of optimum temperatures, in which the work of 

 Sachs and Haberlandt is largely drawn upon. 



Acclimatization is touched upon only briefly, for 

 the most part with reference to Mayr's contri- 

 butions. For the general reader one or two 

 re-statements are interesting : that no portion of 

 the earth's surface is too cold for plant life, as, 

 with few exceptions, no portion is too hot ; that 

 it is nowhere too dark, nowhere too bright, for 

 plant life. There is opportunity to take ex- 

 ception to the sweeping nature of these state- 

 ments, but they are hardly intended to be taken 

 as absolute. Under atmosphere is considered 

 atmospheric pressure, air content of water and 

 winds. The relatively much greater effect of 

 the wind upon woody formations is pointed out, 

 as also the influence of the wind upon transpira- 

 tion. No mention is made, however, of the 

 action of the wind in dune regions, sandhills 

 and deserts, where it plays a primary role in 

 the determination of the floral covering. The 

 importance of winds in pollination and dis- 

 semination is treated briefly. 



The chapter upon soil as an ecological factor 

 is very skillfully summarized. Though brief, it 

 is so comprehensive that recapitulation is im- 

 possible here ; one can only reafflrm its ex- 

 cellence. The influence of animals upon vege- 

 tation has not been given as much attention as 

 would be expected. Too little use has been 

 made of the vast accumulation of data in this 

 field. In many instances the ecological signifi- 

 cance has not been fnlly wrought out. More- 

 over, a large number of important biological 

 factors in ecology, arising from the interrela- 

 tions of plants to plants, and of plants to the 

 physical conditions, such as vegetation pressure, 

 zonation, layering, etc., have been entirely 

 neglected. 



It is impossible to accept the author's group- 

 ing of formations into climatic and edaphic in 

 the absolute way he seems to intend it. Forests, 

 prairies and deserts are not purely, nor always 

 primarily, determined by climatic factors. The 

 so-called edaphic formations, determined 

 though they are by soil characteristic, are often 

 not formations, but zones or patches. They 

 are but rarely coordinate with the author's 

 climatic formations. The conception of the 

 facies, moreover, differs from that of Drude, 

 which has been accepted in this country. The 

 division of the floral covering into forests, 



