898 



SCIENCE 



[N. S. Vol. XL. No. 1.M2 



grasses cover the soil between the trees. This 

 difference in the types of plant covering on the 

 windward and leeward sides is the most strik- 

 ing feature of the distribution of the vegeta- 

 tion of these mountains. A comparison of the 

 vegetation of a valley bottom with that of its 

 own higher bounding slopes, even on the be- 

 clouded windward side, shows a difference of 

 the same sort as that just mentioned, thoiigh 

 somewhat less marked. 



Detailed instrumental measurements of the 

 physical characteristics of several selected hab- 

 itats were made by Shreve, between October, 

 1905, and June, 1906. These studies of the cli- 

 mate, in the valleys and on the ridges and at the 

 top of the forest canopy as well as on its floor, 

 together with his inquiry into the transpira- 

 tion capacity of typical rain-forest plants, are 

 perhaps the most unique features of his con- 

 tribution. The habitat in which the climatic 

 peculiarities of the rain-forest are most ac- 

 centuated, as was demonstrated by the aid of 

 the air and soil thermographs, the hygrometer 

 and atmometer, is the floor of the windward 

 ravines. Here soil moisture is abundant, the 

 leaves are dripping wet with rain or fog for 

 weeks together. The humidity is constantly 

 high; the rate of transpiration is very low 

 and the light filtering through the screen of 

 foliage and of cloud is faint even at midday. 

 On the slopes, and especially on the ridges, of 

 both windward and leeward sides of the moun- 

 tains, where air currents and sunlight have 

 freer access, the soil is still moist, but the 

 leaves are less often covered with water drops, 

 and measurement shows that the humidity of 

 the air is less, the rate of transpiration is 

 higher and there is a somewhat greater daily 

 range of temperature. These climatic differ- 

 ences, taken together with the characteristic 

 differences in the vegetation of the two sides 

 of the range, make it clear that the general 

 distribution of the vegetation here is controlled 

 primarily by the moisture content of the air 

 rather than by that of the soil. The latter is 

 probably adequate in all but a few restricted 

 locations. 



One very interesting feature of the seasonal 

 activity of the rain-forest trees is that while 



certain of them vegetate actively throughout 

 the year, others growing right beside them show 

 a well-marked winter rest. Most of the former 

 species are allied with the lowland tropical 

 forms, while the latter are allied rather with 

 north temperate genera. 



Most plants of this montane region grow 

 quite slowly, probably in consequence of the 

 moderate temperatures, a low transpiration 

 rate and the often weak light. The uncoiling- 

 leaves of certain ferns show the most rapid 

 growth observed. 



The rate of transpiration was studied in 8 

 or 10 species. One rather unlooked for result 

 was that the rate of transpiration for these 

 plants, under the conditions prevailing in the 

 rain-forest, is not very unlike that found for 

 many Arizona plants when growing under 

 desert conditions. As a matter of fact the 

 desert plant, in spite of its highly protected 

 surface, loses more water per square centi- 

 meter of surface, in its native habitat, than 

 the plant of the rain-forest when growing in 

 its home. 



One other interesting conclusion of the 

 author from this comparison of rain-forest 

 plants and desert plants is that the continuous 

 extreme humidity, the low temperature and 

 weak illumination give conditions approxi- 

 mately as unfavorable to plant growth as are 

 the opposite extreme conditions of arid regions. 

 The tropical lowlands and the moist temperate 

 regions are regarded as the homes of the most 

 luxuriant and most varied floras of the earth, 

 and the places of origin of new structures and 

 new species. 



Duncan S. Johnson 



Engineering Geology. By Heinrich Eies and 



Thomas L. Watson. New York, John. 



Wiley & Sons. Octavo, bound in cloth. 



672 pages. 



This volume fills a special field in which it 

 has no rival. It is arrS'iged particularly for 

 the use of the student of civil engineering, 

 but the full treatment of many subjects and 

 the extensive lists of standard papers will 

 make it also a valuable reference work for 

 engineering libraries. In many engineering 



