JASUAEY 11, 1S95.] 



SCIENCE. 



53 



The address on the opening of the Baugor 

 Laboratories will be of interest to all who 

 have to do with their like ; that on the occa- 

 sion of the unveiling of Joule's statue will 

 interest everybody who cares for or who 

 knows of the greatest generalization of 

 modern science. In short, every page of 

 this volume is deserving of the careful 

 perusal of all who are devoted to Natural 

 Philosophy in its most comprehensive sense, 

 and wlio wish to know something of the 

 spirit of one whose splendid contributions 

 to physical science are, as a whole, greater 

 than those of any other philosopher of the 

 present time. 



The mechanical execution of the book 

 does not seem to be quite in keeping with 

 the classical character of its contents, and 

 its pages are occasionally man-ed by negli- 

 gent proof reading. T. C. Mendenhall. 



Worcester Polytechnic Ixstitute. 



Lair.-t of Temperature Control of the Geographic 



Distribution of Life. 



In the Decemlier issTie of the National 

 Geographic Magazine, Dr. C. Hart Merriam 

 announces the discovery of the laws of 

 temperature control of the geographic dis- 

 tribution of terrestrial animals and plants. 

 Dr. Merriam has Ijeen engaged on this 

 problem for sixteen years and believes he 

 has at last obtained a formula which ful- 

 fills the requirements. He states that in 

 the Xorthern Hemisj)herc animals and 

 plants are distributed in circumpolar belts, 

 the boundaries of which follow lines of 

 equal temperature rather than parallels of 

 latitude. Between the pole and the eciuator 

 there are three pi-imary belts or regions — 

 Boreal, Austral and Tropical. In the 

 United States the Boreal and Austral have 

 each been split into three secondary trans- 

 continental ztmes, of which the Boreal are 

 known as the Arctic, Iludsonian and Cana- 

 dian ; and the Austral as the Transition, 

 Upper Austral and Lower Austral. 



Tlie teni])eraturt' data computed and 

 plotted on maps as isotherms are not avail- 

 able in locating the boundaries of the zones, 

 because thej- show the temperature of arbi- 

 trary periods — periods that have reference 

 to a particular time of year i-ather than a 

 particular degree or quantity of heat. 



It is assumed that the distribution of 

 animals and plants is governed l)y the 

 temjjerature of the season of growth and 

 reproductive activity — not by that of the 

 entire jear. The difficult}' is to measure 

 the temperature concerned. 



Physiological botanists have long main- 

 tained that ■■ the various events in the life 

 of plants, as leafing, flowering and matur- 

 ing of fruit, take place when the plant has 

 been exposed to a definite quantity of heat, 

 which quantity is the sum total of the dailj' 

 temperatures above a minimum assumed 

 to be necessary for functional activity." 

 The minimum used by early botanists was 

 tlie freezing point (0° C or 32° F). but re- 

 cent writers believe that 6° C or 42.8° F 

 more correctly expresses the temperature of 

 the awakening of plant life in spring. '• The 

 substance of the theory is that the game stage 

 of vegetation i< attained in any year when the 

 sum of the mean daily temperatures reaches the 

 same value, which value or total is essentially 

 the same for the same plant in all localities. 

 This implies that the period necessary for 

 the accomplishment of a definite physio- 

 logical act, blo.ssoming. for instance, may be 

 short or long, according to local climatic 

 peculiarities, but the total quantity of heat 

 must be the same. The total amount of 

 heat necessarj' to advance a plant to a given 

 stage came to be known as the physiological 

 con-ftant of that stage." But .students of 

 geographic distribution are not concerned 

 witli the physiological constant of any stage 

 or period in the life of an organism, but 

 with the physiologicnl constant of the species it- 

 ,^,,lf — if such a term may be used. " If it 

 is true that the same stage of vegetation is 



