No. 4, January, 1921| ECOLOGY, PLANT GEOGRAPHY 219 



extreme xerophytism. Cribbs has measured the factors of these habitats, including tempera- 

 ture, evaporation, humidity, soil moisture, and soil temperature, and has presented his 

 results in a series of graphs exhibiting the range of mesophytism characteristic of the different 

 habitats. In each of these habitats he lias measured the foliar transpiring power of leaves of 

 the same age and similar position, using the cobalt chloride paper method. These results are 

 presented in graphs which express as some of the most notable of the results: (1) The foliar 

 transpiring power increases from that indicated by an index of 0.15 in the mesophytic forest 

 situation to that with an index of 0.55 in the most exposed situation on the open sand. (2) 

 In the forest the daily march of relative transpiration is represented by a curve with a single 

 mode developing about midday and coinciding with the maxima of temperature, relative 

 humidity, and evaporating power of the air. (3) In more exposed situations the transpira- 

 tion curve becomes bimodal, with the maximum appearing earlier in the day than the maxima 

 of temperature, relative humidity, and evaporation. (4) The second mode developing in the 

 afternoon is always lower than the mode preceding the depression due to saturation deficit. 

 (5) No evidence of visible wilting occurred in Tilia on the open sand at any time during the 

 summer, although the so-called "incipient drying" was a common feature of the stations 

 throughout this period. On the forested complex, however, visible wilting occurred during 

 the first week of August because the vegetation was so dense that the water content of the 

 soil was reduced quite early to a point below the wilting coefficient. (6) The amount of water 

 in the soil apparently has very little influence on the transpiration index unless it is reduced 

 to the wilting coefficient. The saturation deficit depression is due to the inability of the 

 translocating system to conduct water to the leaves with sufficient rapidity to offset the 

 transpiration loss — Geo. D. Fuller. 



1499. Gleason, Henry Allan. Some applications of the quadrat method. Bull. Torrey 

 Bot. Club 47: 21-33. 1920. — The quadrat method constitutes the only practical means for 

 quantitative study of the plant association and is of great importance in correcting the 

 deficiencies of written description and photography. There are quadrats of various types: 

 a simple list of species, the number of individuals of each species, and the map type in which 

 a chart is prepared on scale. A single quadrat is apt to give a one-sided picture of an asso- 

 ciation because of lack of homogeneity within the association; the chief value in this method, 

 then, lies in the use of many quadrats, the size of which must be determined by the general 

 character of the vegetation. The first quadrat used can be located anywhere; succeeding 

 ones can be at definite distances from the first to avoid personal choice. At the conclusion 

 of the count, the ratio between the total number of quadrats and the number in which a 

 given species occurs is expressed as a percentage which is known as the frequency index (FI). 

 Some rarer species will thus be missed entirely, but those of actual importance in the asso- 

 ciation will be counted. There is a definite relation between the number of individuals of a 

 species and its frequency index. If n plants are scattered at random over q quadrats the 



probability of any one quadrat being occupied is expressed by the formula 1 — ( J . 



But since plants are not distributed entirely at random, the actual number is greater than 

 indicated by the mathematical formula. Since the frequency index increases with the size 

 of a quadrat, a major quadrat may be chosen which will normally include all the more im- 

 portant species. The proper size of this major quadrat may be determined by reducing the 

 original series of quadrats to a smaller number of larger ones by substituting in the formula 



FI = 1 — (1 )", for q the number of quadrats actually counted, and for FI the index of 



the least common of the important species. Jaccard's community coefficient is shown to be 

 unsatisfactory in allowing equal weight to small slender plants and to larger ones; it might 

 be improved by a multiplier expressive of size. — P. A. Munz. 



1500. McLean, R. C. Studies in the ecology of tropical rain forests, with special refer- 

 ence to the forests of South Brazil. Jour. Ecol. 7: 121-172. 10 fig. 1919.— This report con- 

 tinues the account of the rain forest near Rio de Janeiro, Brazil, already noted (see Bot. Absts. 



