No. 1, July, 1920] ECOLOGY, PLANT GEOGBAPHT -< 



for San Diego for the same period is very similar to thai of tie- Imperial Valley, although 

 it is over ion miles away. The conclusion is reached that no appreciable influence upon the 

 course of humidity through the season is exerted by the amount of irrigation water used. 

 Seasonal humidity fluctuations are to be accounted for through geographically far-reaching 

 meteorological factors. — Chas. .1. Skull. 



196. McLean, R. 0. Studies in the ecology of tropical-rain forest: with special reference 

 to the forests of south Brazil. I. Humidity. Jour. Ecol. 7: 5-54. 21 fig., 1 pi. May, 1019. — 

 This work was done in the rich forests on the slopes of the hills near Rio de Janeiro, Brazil, 

 a region shown to possess a high average humidity, a mean rainfall of 111.2 cm. (the heaviest 

 rains occurring during the hot months), and a very considerable amount of cloudiness wh'ch 

 is also at its height during the hot season. The combination into a single graph of the factors 

 of temperature, rainfall, relative humidity, and sunshine proves the climate to be decidedly 

 periodic, with the most favorable portion of the year for plant development falling within the 

 months extending from December to May. Graphs show that the relative humidity is al- 

 ways high not only within the forest at heights of one and four meters above the soil, but also 

 outside the forest and above the foliage-canopy. Thermographic studies within the forest 

 disclose the fact that the dense layer of terrestrial shrubs seems to divide it into two portions, 

 the lower possessing a climate decidedly cooler and more humid than the brighter regions 

 above. The author conceives that this lower stratum possesses the conditions most unfavor- 

 able to vegetation and to it his experimental work is confined. — Experiments show that the 

 highest rate of water loss by transpiration from shade leaves in the lower stratum of the 

 forest is never greater than 0.4 of the evaporation from a free water surface exposed under 

 exactly similar conditions. Transpiration experiments conducted in the laboratory with 

 atmospheric saturation and strong light gave very similar results. Cuticular transpiration 

 from the shade type of leaf is shown to be very slight on account of a rather remarkable amount 

 of cutinization. A comparison of the shade and the sun form of leaves on the basis of inter- 

 cellular space relative to leaf mass shows that in the former it amounts to 24.8 and in the 

 latter to 16.3 per cent. Data were obtained upon the number and size of stomata for under- 

 growth plants and seem to show that both are rather smaller than in the typical mesophytes 

 of temperate lands. The vascular strands of the petioles of the leaves of such plants are 

 found to be much smaller than those in sun species. These and other data tend to show that 

 in the shade leaves of the forest both the power of root absorption and of conduction are de- 

 cidedly small and most inadequate to the transpiration capacity of the leaves, hence trans- 

 piration even in the protected region of forest undergrowth may, for short periods at least, 

 rise above the low capacity of the plant to supply water. This the author interprets as lead- 

 ing to the development of protective devices even in a very moist habitat. — Under such con- 

 ditions of depressed transpiration there is, however, no shortage of mineral matter, but on 

 the contrary the leaves of the shade habitats show a relatively richer content than do the 

 heliophytes, proving that here, at least, the absorption of mineral salts is quite independent 

 of foliar evaporation. — In addition to these experimental results there appear in the paper 

 many observations of interest among which may be cited records of the abundance of pulvini, 

 the predominance of the lanceolate leaf-form and the non-importance of the drip-tips of the 

 foliage. — Geo. D. Fuller. 



197. Pavillard, J. Les progres de la nomenclature dans la geographie botanique. [The 

 development of nomenclature in phytogeography.] Ann. Geog. 27: 401-415. 191S. — The author 

 begins with an historical and critical sketch of the conditions of the past and then proceeds 

 with an analysis of the scope of plant geography. Here it is suggested that it would be desir- 

 able to follow the practice of the Swiss school and employ the designation "geobotany" sug- 

 gested by Grisebach in 1866. Resting upon the two fundamental unities of the species and 

 the association, two main divisions of the science are then made, the one termed geobotany 

 the other plant sociology or phytosociology. Each of these is further subdivided into three 

 parts, giving as the subdivisions of the subject: (1) Floristic geobotany; (2) Genetic geo- 

 botany; (3) Ecologic geobotany; (4) Floristic phytosociology; (5) Genetic phytosociology ; 

 and (6) Ecologic phytosociology. — Geo. D. Fuller. 



