June 10, 1904.] 



SCIENCE. 



885 



botanical section of the British Association 

 on the geographic distribution of past 

 floras, Wieland's novel but not new view 

 as to the polar origin of life, and Schulz's 

 papers on the geological development of 

 the flora of the Saale and the Suabian Alps. 

 In closing, a word may be said as to the 

 present status of Briquet's poly topic 

 theory, a theory commonly discarded as 

 untenable, but which the mutation theory 

 and the growing belief in polyphylesis make 

 more probable. The idea that a species 

 may originate in more than one place, 

 simultaneously or not, did not originate 

 with Briquet, but he resuscitated it and 

 christened it the polytopie theory. Though 

 discarded by Jerosch and most writers, as 

 unlikely if not unthinkable, Willis believes 

 that the same step might be taken by species 

 that are far apart, especially in similar 

 conditions; indeed he thinks that this has 

 actually happened within the Podostema- 

 cea. Arber has favored the idea of 

 homeomorphy or parallelism of descent. 

 Engler has admitted that varieties may 

 originate more than once. It Avill be re- 

 called that in DeVries's experiments the 

 same species recurred many times, and that 

 too from different parents. Blackman has 

 found that about twenty per cent, of the 

 arctic and antarctic algse are identical as 

 to species, but not found elsewhere. It 

 will be conceded that in such a case the diffi- 

 culties in the way of migration during the 

 present or past ages are very great, while 

 the polytopie theory seems to afford an easy 

 explanation. Perhaps it is too easy; in 

 any event it seems adapted for use as a last 

 resort rather than as a general panacea. 

 HoM^ever, the researches of the past few 

 years have placed the theory of polytopie 

 origins in a position to demand the thought- 

 ful consideration of all students of evolu- 

 tion. 



Henry Chandlee CowIjES. 



BCIENTIFIG BOOKS. 

 Desert Botanical Lahoratory of the Carnegie 

 Institution. By Frederick V. Coville and 

 Daa^iel Trembly MacDougal. Published by 

 the Carnegie Institution. Washing-ton, No- 

 vember, 1903. Pp. 58, with 29 plates and 

 4 charts. 



This attractive account of a botanical recon- 

 noissanee of the desert areas of the southwest 

 will, without doubt, awaken great interest in 

 desert vegetation, and stimulate the thorough 

 investigation of the adaptations of xerophytes. 

 The debt which ecology owes to Drs. Coville 

 and MacDougal for fostering the idea of a 

 desert laboratory, and for carrying it to a suc- 

 cessful conclusion must become more and 

 more apparent as the work progresses. The 

 report deals in a very interesting though neces- 

 sarily general fashion with the vegetation of 

 the areas visited in connection with the loca- 

 tion of the laboratory. These were: (1) The 

 arid region of western Texas; (2) the sand 

 dunes of Chihuahua; (3) the White Sands of 

 the Tularosa Desert; (4) the vicinity of 

 Tucson; (5) the g-ulf region about Torres and 

 Guaymas; (6) the Colorado Desert; (Y) the 

 Mohave Desert; (8) the Grand Canyon of the 

 Colorado. 



In many ways the most interesting region 

 to the ecologist is that of the White Sands of 

 the Tularosa Desert. These are for the most 

 part mobile dunes, composed entirely of gyp- 

 sum; they cover nearly four hundred square 

 miles. The soil is necessarily alkaline, a fact 

 clearly indicated also by the abundance of 

 Atriplex and Suceda. The characteristic vege- 

 tation of the dunes consists of woody plants, 

 chief of which are Rhus trilohata, Atriplex 

 canescens, Chrysothamnus and Yucca radiosa. 

 Yucca, by virtue of its striking ability to pusk 

 up through a sand cover, is a typical dune 

 former. The White Sands when critically in- 

 vestigated should add an interesting chapter 

 to the developmental history of dunes. The 

 selection of Tucson for a laboratory site was 

 based upon the variety and distinctness of its 

 desert ilora, as well as iipon its being both 

 habitable and accessible. The vegetation in 

 the neighborhood of Tucson consists mostly 



