June 3, 1910] 



SCIENCE 



865 



this view, and while no detailed study is as 

 yet available, it is pointed out that vigorous 

 competition is the rule and not the exception. 

 The " mutual accommodation " of certain 

 plants as seen in the non-interference of the 

 root systems (Cannon) is referred to; thus, 

 the proximity of certain species involves the 

 minimum of competition. Accommodation 

 appears to the reviewer, therefore, as to Dr. 

 Cannon, to be a minor degree of competition, 

 or at least involves at some tim.e a struggle. 

 It frequently happens, e. g., that the sheltering 

 protection of an established plant results only 

 in establishing active competition, frequently 

 of minor but often of greater vigor, between it 

 and its protege. In this connection is of in- 

 terest an account by Dr. Cannon, of the root 

 system of Cereus (Carnegiea) giganteus and 

 its mutual relations with those of three other 

 species, discovering important topographic 

 differences, which result that the roots of these 

 plants, growing close together, are rarely in 

 physical contact, because, chiefly, they do not 

 occupy the same soil horizon, though " this 

 does not mean that the plant (Cereus) is free 

 from competition." It is further developed 

 that the cacti are chiefly characterized by a 

 relatively much more important lateral, shal- 

 low root system, and sees in this an important 

 adjustment for aeration, in the absence of 

 foliage, as well as to mechanical support, and 

 for the remarkable readiness with which 

 slight precipitation is made use of. 



Professor C. F. Tolman gives an account of 

 the geology of the vicinity of the Tumamoc 

 Hills, where stands the laboratory. Two mat- 

 ters of more general interest emerge, namely, 

 the origin of the wide slopes of gentle gradi- 

 ent, above referred to, and that of the " cal- 

 iche," the calcareous hard-pan which plays an 

 important role in its relation to the vegeta- 

 tion. Professor Tolman contends for the sub- 

 aerial deposition of the elinoplains (Herrick) 

 or conoplains (Ogalvie) and applies to these 

 the simple, but unfortunately generic name of 

 " slopes," to which the reviewer had previ- 

 ously applied the more specific term, foot-slope. 

 To him — perhaps for human reasons alone — 

 the latter appears the more descriptive and ap- 



propriate name. But we are more interested 

 in Professor Tolman's views — concerning the 

 materials composing the slopes. They are de- 

 rived from the steeper mountain slopes abeve, 

 which are, under semi-arid conditions, strongly 

 attacked by torrential precipitatien. The 

 slope is, as said, of sub-aerial origin, in the 

 formation of which temperature change and 

 gravity play the leading parts, running water 

 bearing " a varying role." This view is as- 

 serted chiefly for the reason that it controverts 

 an earlier interpretation which calls upon a 

 former marine or lacustrine extension to ex- 

 plain the topographical uniformity of the 

 foot-slopes. Professor Tolman says that " de- 

 position " in the playa is " most active during 

 periods of water occupancy, when the dust 

 from the mountains and slopes is caught by 

 the water sheet." The evaluation of the fac- 

 tors at work is, however, confessedly difiicult, 

 but the reviewer suggests that, in undrained 

 playas, the moving water sheet on the lower 

 zones of the foot-slopes and the arroyo-im- 

 prisoned streams of their upper zones, conse- 

 quent on heavy precipitation, are of great im- 

 portanrce in eroding and carrying finer de- 

 tritus to be laid down by the standing water 

 sheet. As a matter of observation, this seems 

 to be an important condition at the present 

 day in certain regions. 



The explanation of the caliche — this, Pro- 

 fessor Blake's name, is retained — accords, with 

 slight modification, with that of Professor 

 Forbes. Caliche is, according to the latter, a 

 " mixture of colloidal clay and carbonate 

 (mainly) of lime," carried by the rain water 

 downward into the soil to the depth, a few 

 inches to three or four feet, where, as the re- 

 sult of desiccation, the hard-pan is formed. 

 Professor Tolman finds, however, a ready sup- 

 ply of calcareous matter, coupled with an ab- 

 sence of drainage to remove it, to favor the 

 encrustation. The rapidity with which caliche 

 may be formed under experimental conditions 

 out-of-doors may be remarkable — two inches 

 in two years. The body of Professor Tolman's 

 paper treats of the topography, geology and 

 petrography (based on the work of Professor 

 F. W. Guild) of the laboratory domain. This 



