C. E. Moss. 
i 84 
dicotyledons respectively, it is found that Bctula ascends to 
higher altitudes and reaches higher latitudes than Pinus. As 
the two species often occur as associates in identical situations, 
this distribution 1 suggests that the xerophily of Betnla is more 
effective than the xerophily of Pinus. 
Rikli, 2 discussing the vegetation of Corsica, gives the conifer 
zone of that island as between 800 and 1,200 metres. In the lower 
part of this zone, Pinus Pinaster is dominant, P. Laricio in the 
upper. Above the conifer zone, however, Rikli records a beech 
zone. In the lower part of the beech zone P. Laricio is present; 
but the deciduous beech ( Fagus sylvatica) reaches 1,400 metres, an 
altitude which is not attained by the evergreen pine (P. Laricio). 
Again, among the conifers themselves, it is the deciduous 
species of Larix that reach the farthest north. Cajander 3 records 
species of Larix at 70° N. on the river Lena, and this latitude is 
not reached by any of the more numerous, evergreen conifers. 
The same phenomenon is seen amongst the dicotyledons 
themselves. The distribution 1 of Callnna, with its markedly 
“ xerophytic leaf,” is less wide than that of Vaccinium Myrtillus , 
with its so-called “ mesophytic leaf”; and, further the deciduous 
Vaccinium reaches a much higher altitude than the evergreen 
Calluna, although these plants frequently occur side by side. 
Again, confining attention to a single dicotyledonous genus, 
each of the two deciduous members of the genus Vaccinium 
(V. Myrtillus and V. uliginosum ) possesses a wider distribution 1 and 
ascends to a higher altitude than any evergreen member of the 
genus (e.g., V. Vitis-Ideea) ; and similarly the deciduous oaks (e.g., 
Quercus Robur) ascend to higher latitudes and altitudes than the 
evergreen oaks (e.g., Q. Ilex and Q. Suber ). 4 
These examples are taken from species which are ecological 
and systematic allies respectively ; and the facts appear to support 
my view that the deciduous habit is a more effective form of 
xerophily than the “ xerophytic leaf ” and “ xerophytic wood ” of 
the conifers. The facts also suggest that when xerophily is under 
consideration, the habit as well as the structure of plants must be 
taken into account. 
1 Smith, R. “ Plant Associations of the Tay Basin ” ; I., Proc. 
Perthshire Soc. of Nat. Sci., 1898 ; II., Ibid., 1900. 
s Rikli, M. “ Botanische Reisestudien auf cincr Friihlings fahrt 
durch Korsica.” Zurich, 1903. 
3 Cajander, A. K. “ Studien iiber die Vegetation dcs Urwaldcs 
am Lena-Fluss.” Helsingfors, 1904. 
4 Flahault, C. “ Essai d’une Carte botanique et forestidre de la 
France-” Ann. de Geogr., 1897. 
