June 30, 1916] 



SCIENCE 



933 



Cyperacese 7 genera and 95 species, Crucifewe 

 28 genera and 69 species, Eosacese 28 genera 

 and 61 species, Leguminosse 13 genera and 72 

 species, Compositse 66 genera and 89 species. 

 The genera containing more than 15 species 

 are : Agrostis 18, Poa 22, Carex Y3, J uncus 23, 

 Salix 19, Polygonum 20, Ranunculus 19, 

 Lupinus 19, Trifolium 20, Epilohium 18, 

 Erigeron 17 and Senecio 17. All of these gen- 

 era with the exception of Trifolium and 

 Lupinus are common not only throughout the 

 cooler parts of ISTorth America, but of Europe 

 and Asia as well. In fact, while there are 

 many endemic species, the general floral ele- 

 ment is that of the Boreal Realm, just as we 

 would expect, since the region lies within the 

 Arctic to Transition zones. Very few of the 

 typical American genera of the arid regions of 

 the west are represented. 



The text is supplied with keys to families, 

 genera and species, but the descriptions of the 

 species are often meager, too much so we fear 

 in some cases for certain identification. But 

 in the reviewer's mind the most disappointing 

 feature of this admirable work is the ex- 

 tremely meager and indefinite distributional 

 notes. It is to be regretted in this respect that 

 the authors did not follow the excellent ex- 

 ample set by the senior author in his " Flora 

 of Washington," and give the zonal distribu- 

 tion. Two additional words would have been 

 sufficient, and these with a little fuller defi- 

 nition of each zone in the preface would have 

 been of great service to the student of plant 

 distribution. 



LeEoy Abrams 



NOTES ON METEOROLOGY AND 

 CLIMATOLOGY 



Professor Alexander McAdie and Mr. Wil- 

 liam G. Eeed have each recently presented sev- 

 eral papers on the meteorology of local frosts, 

 the causes of frost damage to plants and meth- 

 ods of protection, the dates of occurrence of 

 frost, and bibliography of frost in the United 

 States. 



The meteorology of frost formation is dis- 

 cussed by Professor McAdie in an article en- 

 titled " Temperature Inversions in Relation to 



Frosts." ^ Two laws of frost formation are 

 enunciated as follows: 



(1) Where the air is in motion, there is less 

 likelihood of frost than where the air is stag- 

 nant; (2) frost is more likely to occur when the 

 air is dry (and dustless) than when it is moist. 



The first is true because local frosts are con- 

 nected essentially with local " air drainage." 

 Soon after sunset, cold and dense air, cooled 

 chiefly by radiation to the ground, drains 

 slowly down the slopes into the valleys and low 

 places. Strong winds mix the air and so pre- 

 vent the occurrence of local frosts. The second 

 law is based on the retardation of temperature 

 change due to moisture in the air. The water 

 vapor strongly absorbs the heat rays from the 

 earth, acting in this way as a blanket. If con- 

 densation occurs, there is further retardation 

 of the cooling by the liberation of latent heat. 

 Since dry air is denser than moist air at the 

 same temperature, a loss or gain of moisture 

 as well as a change in temperature affects the 

 rate of " air drainage." To obtain a continu- 

 ous record of the weight of water vajwr in 

 grams per cubic meter of air. Professor Mc- 

 Adie has devised a " saturation deficit re- 

 corder." This instrument is essentially a 

 hygrograph mounted on the pen of a thermo- 

 graph. The thermograph indicates the maxi- 

 mum weight of water vapor possible in the air 

 at the temperature prevailing, and the hygro- 

 graph indicates the percentage of saturation. 



Protection of plants from injury by frost in- 

 volves the conservation of the earth's heat 

 with covers, the addition of heat to the air, or 

 the use of some agency with high specific heat, 

 such as water, to prevent cooling. Preventable 

 damage often results from too rapid defrosting 

 in the morning; fortunately, the same agents 

 which keep the temperature from falling re- 

 tard its rise. 



Mr. Eeed treats the subject of protection as 

 a whole in an illustrated article, " Protection 

 from Damage by Frost." ^ The methods most 

 successful commercially depend upon the com- 



1 Annals, Harvard College Observatory, Vol. 73, 

 pp. 168 to 177, 4 pi., Cambridge, 1915; or see 

 Scientific Monthly, December, 1915, pp. 293 to 301. 



2 Geographical Beview, February, 1916, pp. 110 

 to 122. 



