146 The Plant World. 



favorable, without by any means being moist. ]\Iy observation 

 of numerous species of desert plants which ha\e l.een artificially 

 irrigated or ]:rotected from extreme insolation shows that there 



is no one of tliem to which a slight amelioration of the atmos- 

 pheric aridity, or a slight increase of the soil moisture, or of 

 the number of tin:es the soil is made wet, does not permit both 

 a greater vegetative and a greater reproductive activity. 

 'I'liese slighth' inijiroved conditions are to be found between 

 ."^000 and 7000 feet altitude in the desert mountains, but they 

 are to be found only where the winter cold conditions are such 

 that desert species are unable to survive. In other words the 

 failure of desert species to establish themselves in a region 

 which seems at first sight to be a more favorable one than that 

 in which they are common, is due to the oj^eration of a factor 

 entirelv distinct from those which have to do with the appar- 

 ent favoral)leness. 



Tlic Desert Lahoralory, 



Tucson. ' 



BOOKvS AND CURRENT LITERATURE. 

 Altittdinal Limits ix .Mkditerraxeax \'egetation — 

 Koch's ''Contributions to Our Knowledge of Altitudinal 

 Limits of \'egetation in the ^Mediterranean Region" '"' 

 emphasises especially and seeks to define the temperature re- 

 lations of the vegetation, although recognizing the concurrent 

 action of oilier factors. In Southern France, the Apenniiie 

 peninsula, the Balkan region, Greece, Asia Minor, Syria and 

 northern .Africa there is observed a horizontal distrilnition of 

 the Mediterranean vegetation, of the forests, and the alpine 

 vegetation and a vertical extension of the Mediterannean veg- 

 tation as a whole and of such representatives as Laiiriis )iobilis, 

 .\l]yht^ ri>iiiiuiiiti\\ I-iuius sy/raiica, Oiicrcus ilex and others. 

 The principal results of the author's studies mav be summa- 

 n/ed as follow,>: In the ^Iediter:anean region a parallelism of 

 the lower and apper limits of ])lants is observed, with depar- 

 tures i\\\ii to local inlluences. 'fhe upper limits are influenced 

 bv tlie temjieratures of June and Jnh. In general the temper- 

 ature of January influences the outline of the upper limit of 



* Koch, M., Bcitrage zur Kentnis der Hohen grenzen dci Vegetation im Mittelmeergebeite 

 Dissertation, Halle, 100 pp. 1909. 



