1898 | THE SIZE OF EVERGREEN NEEDLES 431 
be shown that there is some pressure under normal conditions, 
present throughout the season of active growth; or that the 
length of the needles varies—as the root pressure probably 
does, if present at all—with the distance from the ground. 
Since the variation from year to year, like the disturbances 
following transplanting, depends upon the general condition of 
the tree, it is self-evident that they will be the same on the main 
axis and on all its branches. 
The most casual observation shows that in this climate the 
needles or leaves formed during any year are at first very short, 
afterward longer, and at the end of the season again short. In 
measuring the needles to find the average length for each year, 
it was immediately apparent that the progression in the length 
of the needles was surprisingly uniform. The first lines of 
figures in the individual tables show this almost as forcibly as 
plotting the curves would do. Each measurement is the average 
of ten successive needles, except in the instance of Pinus Aus- 
iriaca, in which ten pairs of needles were taken. The figures at 
the beginning of each line represent the lowest needles on the 
year’s growth of stem. Ten leaves taken each time is too many 
to show the curve in any detail when the year’s growth bears as 
few leaves altogether as in the instances of Tsuga and Taxus; 
but on branches so conspicuously dorsiventral the leaves borne 
on the under side are so much longer than those above that 
taking a smaller number each time yields too broken a curve. 
The series of needles still clinging to stems more than three 
Years old is usually quite incomplete, but except in one or two 
cases I have been unable to see that the shorter needles were 
cast off before the longer.? 
The numbers representing the needle lengths advance each 
year from the spring minimum to a maximum, usually near the 
middle of the yearly growth in length, and then decrease to the 
fall minimum, which is usually lower than the first one. In 
Many of the tables there is no break in the rise or fall, and what 
°S. Honpa, loc. cit: On species of Pinus he found the smallest leaves formed 
latest each year, and seldom clinging more than one year to the stem. 
