No. 1, February, 1921] PHYSIOLOGY 59 



The value of hx corresponding to the integral value 0.5 {vide probability integral table) 

 is 0.4769. Then 



_ iv +0.3623 



X = 0.4769 (10) 2 (7) 



which gives the probable error of a single observation. The probable error of the mean is 

 equal to the probable error of one observation divided by the square root of the total number 

 of observations, 



X 0.4769 , . _ ^±M^ 



X(i — 



= — r^- (10) 2 (8) 



Vn Vn 



In the case of skew frequency distributions the above equations do not strictly apply 

 because of a preponderance of either positive or negative errors. For such cases the equation, 



^ = e-^<'-?J. (9) 



y 



is proposed. Here m represents the numerical value of any measurement and mo the value of 

 the geometric mean. This may be transformed into the equation, 



log - = 2.303 h^ (log — Y (10) 



or 



log ^" = xflog ^Y ... (11) 



y \ mo/ 



Numerous examples of the use of the equations are given, in which the values obtained 

 are compared with those computed by other methods. — H. S. Reed. 



DIFFUSION, PERMEABILITY 



397. Priestley, J. H. Root pressure. [Abstract.] Rept. British Assoc. Adv. Sci. 

 1919:337. 1920. 



WATER RELATIONS 



398. Harris, F. S. The effect of soil moisture on the morphology of certain plants. 

 [Abstract.] Utah Acad. Sci. 1 : 65. 1918. 



399. Livingston, Burton E., and Riichiro Koketsu. The water-supplying power of 

 the soil as related to the wilting of plants. Soil Sci. 9:469-485. 1920.— Plants of Coleus 

 blumei and Triticum sativum grown in 12 mixtures of varying amounts of glass sand, clay 

 loam, and humus, were allowed to wilt until permanent wilting was evident. Dry, unglazed 

 porcelain cones ("soil points") were then thrust into the soil and the amount of water which 

 they absorbed in a given length of time ("water-supplying" power of soil) was determined by 

 removing and weighing. This amount for a 2 hour period was from 0.04-0.11 g. The 

 average value was the same for both plants and practically the same for all 12 soils. — W. J. 

 Robbins. 



400. Zeller, S. M. Humidity in relation to moisture imbibition by wood and to spore 

 germination on wood. Ann. Missouri Bot. Gard. 7: 51-74. 1 pi, 5 jig. 1920.— The rnoisture 

 contents of wood at various atmospheric humidities are presented, the temperature being held 

 at 25°C. Graphs are given to illustrate the relation between water content and humidity, 

 for sap and heart-wood of both longleaf and shortleaf pine. By testing at various humidities 

 the moisture content of any one species of wood, it was possible to approximate the fiber- 

 saturation point. The moisture-humidity curves of highly resinous samples illustrate the 



