DURATION OF LEAVES IN EVERGREENS 1 47 
Hoffman (7), for a series of years prior to 1878, carried on inves- 
tigations with angiosperm evergreens in the Botanical Gardens at 
Giessen. He tied tinfoil tags to the petioles of six or eight leaves on a 
given plant and observed these individual leaves at stated intervals, 
reporting for several species the leaf duration in months. The method 
was too cumbersome to be applied on a very large scale, therefore 
his general conclusions seem hardly justified. 
Kraus (8), in 1880, published on the duration of evergreen leaves. 
Unfortunately his work was not accessible to the writer. 
Other writers, as Copeland (i) and Groom (4), also speak of leaf 
duration. Galloway (3), in 1896, enumerates various factors which 
may affect leaf duration in Pinus virginiana; but these references are 
all incidental, and mentioned in connection with other problems, or in 
general descriptions. 
Sargent (13) (14) and Sudworth (17) in their descriptions of North 
American and Pacific Coast trees mention the leaf duration of many 
species, but their figures do not hold in some cases for the regions 
under discussion, and they give no estimates for other species which 
are quite common in this region. 
The method of determining the age of a given leaf was simple. In 
those species having covered buds, the scars marking the boundaries 
of annual growth made it easy to count the years. In those species 
with naked buds, as Thuja plicata and Juniperus scopulorum, free- 
hand sections were made through the twig at the base of the given leaf, 
and the annual growth-rings of the twig counted under the hand lens 
or low power of the compound microscope. This method was also 
used as a check in other doubtful cases. 
When counting by means of terminal bud scars, the endeavor was 
to make counts of 100 twigs, but that was not always possible. In 
no case, however, did the count fall below 65. When counting by 
means of sections the attempt was made to obtain counts of 50 twigs. 
This was done in a majority of cases, and in no case did the count fall 
below 24. These counts were made in the field whenever possible; 
or the material was collected and carried to the laboratory, where the 
counts were made immediately, before handling dislodged leaves, or 
the unaccustomed dryness of the atmosphere caused them to fall. 
The counts were afterwards tabulated, and the tabulations placed on a 
percentage basis, the percent being calculated to the nearest whole 
number. Finally, curves were plotted from these data {figs. 1-13), 
