Al'KIL 28, I9I0] 



NATURE 



251 



.malysis of the conditions prevailing and determining 

 the precise local distribution of species and communi- 

 ties, including the changes taking place in the 

 arrangement of the vegetation by colonisation and i 

 invasion. <, 



In the various sections of the volume under review, 

 interspersed in the discussion of general principles, we 

 find many interesting details regarding certain species 

 that we can piece together. For instance, we learn 

 that the giant cactus, Cereus giganteus, which raises 

 its fluted columnar stem up to a height of fifty feet, 

 was shown bv Mrs. E. S. Spalding to act as a vast 

 expanding and contracting reservoir, as its ribs and 

 furrows permit of bellows-like action. This plant, like 

 some other desert-plants, possesses extensive shallow 

 roots, which are very efficient collectors of water 

 derived from feeble showers; for Mrs. Spalding found 

 that after a rainfall of 05 inch '" the stems expanded 

 steadilv for three weeks." Such a slight fall of rain 

 would cause an appreciable increase in moisture only 

 to a depth of less than four inches, so that the utility 

 of shallow roots is clearly demonstrated, although so 

 manv desert plants have extraordinarily deep, rela- 

 tivelv unbranched roots. In connection with the ques- 



FiG. 2. — Left side of gulch near Laboratory, with generally north exposure, 



tion of water supply. Dr. Livingston, in his valuable 

 article on the soils, shows by means of curves that the 

 eftects of atmospheric precipitation on moisture in 

 the soil regularly '"lag" behind the actual falls of 

 rain, so that, with certain depths of root, the plant 

 does not immediately profit by showers, nor does it 

 suffer, pari passu with absence of rain, from lack of 

 supply of water. To return to the consideration of 

 Cereus giganteus, Mr. J. C. Blumer clearly shows 

 that individuals of this species, as of certain others, 

 are more numerous on the southern slopes of hills. 

 Inasmuch as other species show a preference for the 

 more favourable northern slopes, there is a difference 

 in the vegetation of the different sides of hills or 

 gulches; and it is shown that on the northern side of 

 the latter' the difference tends to become accentuated 

 with time, because the more numerous individuals 

 and species present tend to cause an accumulation of 

 humus and a consequent amelioration of the soil. 



The section of the volume dealing with the geology 

 of the desert, written by a geologist. Prof. Tolman, 

 seems in subject-matter rather out of place, as it 

 abounds in diffuse and irrelevant generalities. Among 

 these the statement that *' Europe is behind America 

 NO. 21 13, VOL. 83] 



in the study of these newer phases of geology " would 

 perhaps have been nearer correctness a dozen years 

 ago. 



One chapter differing from the others in being not 

 particularly applied to Tucson desert is that on the 

 origin of desert floras, written by Dr. D. T. 

 MacDougal, who deals rather with the possible mode 

 of evolution of biologic types than with the origin of 

 the desert flora. He affirms that consideration of the 

 known facts " leads to the inevitable conclusion that 

 the form-characters, moisture-conserving capacities 

 and resistance to desiccation, distinction of xerophytic 

 species, must have made their appearance within 

 comparatively recent geologic time." In the light of 

 the geological evidence suggesting the former exist- 

 ence of deserts, and in view of the difficulty of 

 geological preservation of the remains of desert-plants 

 (except in oases or by rivers), such a conclusion seems 

 open to the gravest doubt ; and scepticism as to its 

 correctness will be heightened by our knowledge, not 

 only of the existence of xerophytic Cryptogamia and 

 Phanerogamia of all ranks, but also of the distribu- 

 tion of such remarkably isolated types of desert plants 

 as Welwitschia and Acanthosicyos. An additional 

 consideration militating against 

 Dr. MacDougal's conclusion is 

 that xerophytic characters are 

 evolved with considerable facilitv, 

 as is demonstrated by the fact that 

 various xerophytic communities 

 (in deserts, for instance) in differ- 

 ent parts of the world generally 

 include a relatively large number 

 of endemic forms that are defi- 

 nitely allied to and derived from 

 the adjacent non-xerophytic flora. 



In congratulating Mr. V. H. 

 Spalding and his collaborators on 

 this valuable contribution to our 

 knowledge of the ecology- of 

 desert-plants, and on supplying 

 ample justification for the founda- 

 tion of a desert laboratory, we 

 may perhaps be forgiven for add- 

 ing a prayer to American botanists 

 that when they use local or popu- 

 lar names of plants, they will, at 

 least on first mention of these, 

 also give the botanical names. 

 The omission of this precaution 

 causes botanists of other countries to lose more than 

 time in the endeavour to learn what plant is being re- 

 ferred to. For instance, early in the volume under 

 review, reference is made without any explanation to 

 the "sahuaro," the '"creosote-bush," "cotton-woods," 

 the '"ocotillo"; yet few, if any, European botanists 

 would know the identity of all these, or that these 

 names represent respectively Cereus giganteus, and 

 species of Larrea, Populus, and of — the reviewer 

 imagined that he remembered the generic name of the 

 last, but has been compelled to interrupt this sentence 

 and waste ten minutes in fruitless search. 



Percy Groom. 



.VL.B7.4A' ARCH.£OLOGY.' 



THE first publication of the Egyptian Department 

 of the Pennsylvania Universit\- Museum, under 

 the direction of Prof. Randall Maciver, is one that 

 shows great promise for the future. Thanks to the 

 enlightened financial support of Mr. Eckley B. Coxe, 



1 "Areika." By R. Randall Maciver and C. Leonard WooUey. With a 

 chapter on Meroitic Inscripiions. bv F. LI. Griffith. Pp. 56+plates 

 (Oxford : 1 ette-press and Plaies printed by Horace Hart at the Univorsity. 

 Press, i9<^.) Price i/. js. net. 



