1915] BROWN—PINUS STROBUS 235 
of yearly elongation is lost after the first year. No attempt was 
made to trace rapidity of growth of white pine roots. Roots from 
the same tree on May 30 exhibited an average growth of 4-5 
inches, but no other material was secured. We can only infer 
from the data at hand that growth in length began as early as 
April 26, possibly much earlier. 
e results of others in regard to the duration of root growth 
are interesting in this connection. REsA (27), after repeated 
observations on root growth, came to the conclusion that there are 
in all roots two periods of root development, one in the spring, 
which occurs mainly before the unfolding of the leaves, and a second 
during September and October. The last persisted through the 
winter in dicotyledons, with many interruptions from time to 
time, but without complete cessation. In conifers, on the other 
hand, there was a decided rest period during January and February. 
WIELER (38) combated Resa’s conclusions and maintained that 
in the autumn, after leaf fall and the resulting lessened demand 
for water, no new roots were necessary. PETERSON (26) worked 
with young and old trees of a number of dicotyledons, as well as 
specimens of Picea excelsa, Pinus montana, and Larix decidua. 
His results in every way substantiate those of REsA and contra- 
dict the conclusions of WreLER. Among other points explained, 
PETERSON points out that there is a period of root elongation which 
may occur in the spring anywhere between February and June. 
In June, and especially in July, elongation gradually ceases. This 
is followed by a reawakening in growth in length from August 
until October and even into November. The author does not 
State in which period growth is more intense. The researches of 
BUSGEN in 1901 (4) and ENGLER in 1913 (6) substantiate in every 
way those of Resa and PETERSON, so it may be concluded that 
there are two periods of elongation, and furthermore, that in white 
pine the first begins in late April and continues into early June or 
even later. 
Secondary growth in underground parts 
Secondary growth in roots, as in stems, begins the first season, 
and once started proceeds in the usual way. Mention has already 
been made of the variability in white pine roots as regards the 
