RELATIVE TRANSPIRATION OF OLD AND NEW LEAVES 
F THE MYRTUS TYPE. 
JoserH Y. BERGEN. 
WHILE making some studies of the transpiration of the coriaceous- 
leaved evergreens of the Neapolitan region, such as Olea, Pistacia, 
and Quercus Ilex, the writer became interested in the question of 
the relative activity in transpiration of their old and new leaves. 
Some results of the measurements made upon them are here set 
down, together with a few words of discussion in regard to the mean- 
ing of the facts observed. 
It is commonly said that the trees and shrubs of the Mediterranean 
region are largely evergreen, but a little examination into their 
characteristics shows that the word “evergreen” should be used to 
describe them only when its meaning is carefully defined. When 
local floras, like Gussone’s excellent catalogue of the plants of 
Ischia, describe such summer deciduous shrubs as Spartium junceum, 
Cytisus scoparius, and Calycotome villosa as evergreens, it would 
seem that any woody plant with leaves which remain green during 
a considerable part of the winter is considered to be an evergreen. 
As a matter of fact, the angiospermous trees and shrubs of the coast- 
wise region about Naples seem to be classifiable, as regards their 
mode of shedding the leaves, into the divisions shown in the 
table* on the opposite page. 
Some of the plants of division I may be described as facultative 
deciduous species; that is, they may retain their leaves almost or 
quite the year around. The Medicago and the Euphorbia above 
named do this when the water supply is abundant. 
The members of division II are more or less covered with leaves 
at all seasons. Those which belong to subdivision 1 show little 
difference in density of foliage dependent on the season. Many, 
however, of subdivision 2 lose nearly all their old leaves soon after 
the new leaves have reached their full size (area). Rhamnus Alater- 
* The table given is jem illustrative and does not embrace nearly all the species 
which the writer has obse 
446 [DECEMBER 
