450 BOTANICAL GAZETTE [DECEMBER 
greater impermeability of young epidermis (several months old) 
than of that which is more than a year old, and to the greater functional 
activity of the younger than of the older stomata. One would a 
priori have expected to find the thicker and more indurated epidermis 
of the older leaves more impermeable than that of the younger ones, 
but in many cases it certainly is not. For instance, the older leaves 
of Nerium were found to lose moisture more than five times as fast 
for equal areas as the younger ones (both with the lower surface 
waxed), and the older leaves of Olea lost moisture nearly four times 
as fast as the younger ones (both waxed below). 
In the table above given the losses from waxed leaves may be a 
little too high relatively to the losses from plain leaves, since the 
former values were obtained after the leaves had. been standing in 
water longer, and therefore, perhaps may have established a better 
transpiration current. But this would not affect the general conclu- 
sions to be derived from the data. 
The leaves of Olea and of Pistacia compared in the last table 
were aged about six months (“young’’) and eighteen months (“‘old”’) 
respectively, and those of Nerium and Hedera were about three and a 
half and fifteen and a half months of age. 
None of the results obtained by the writer in transpiration experi- 
ments upon sclerophyll leaves can be much elucidated by comparison 
with the conclusions (contradictory among themselves) obtained 
in the studies of young and old leaves by SCHIRMER, KRUTITZKY, 
TscHAPLowi1z, H6HNEL, and others,‘ since none of these authors 
dealt with leaves which differed in age by an entire year. It is also 
unlikely that sclerophyll leaves should in their behavior as regards 
transpiration closely resemble the leaves of the herbaceous Gramineae, 
those of Coleus, Phaseolus, Pisum, and such other species as have 
received most study with reference to the relation between their 
development and their power of transpiration. 
CONCLUSIONS. 
ar conclusions of the present paper may be aaa as follows: 
. The evergreen trees and shrubs of the Neapolitan region differ 
eile in the longevity of their leaves, some of the species having 
4 Summarized by BuRGENSTEIN, Materialien zu einer Monographie betreffend 
die Erscheinungen der Transpiration der Pflanzen. II Theil, pp. 25, 26. Wien. 
1889. A. Hélder. 
