Feb. 1, 1925 
Sowing and Planting Season for Western Yellow Pine 251 
under “Spring sowing.” The effect of 
time of sowing upon time of germina¬ 
tion has been given, and plant develop¬ 
ment, as shown in Table I, also has a 
bearing on the answer to this question. 
The ratio of tops to roots by weight 
was 4 per cent larger for fall-sown 
plants in this case; in other cases it has 
been found to be 8 per cent larger. 
The fact that fall-sown plants become 
more “top-heavy” is believed to be 
the key to the explanation sought. 
When plantings are made in late 
October, the soil surrounding the roots 
remains at a temperature 4 5 low enough 
to retard water intake by any absorb¬ 
ing surfaces left intact by the planting 
act. In the meantime transpiration 
from the tops proceeds, the draft being 
made chiefly upon the moisture con¬ 
tained in the seedlings when planted. 
Gradually the saturation deficit is in¬ 
creased until death or a weakened con¬ 
dition, which handicaps the plant the 
following spring, results. The greater 
the transpiring surface in proportion 
to the absorbing surface present and 
able to function, the faster the drying 
process proceeds with its injurious or 
fatal results. Following spring plant¬ 
ing, conditions are quite different. 
New absorbing surfaces are believed 
to develop after planting, thus pre¬ 
venting any long break in water ab¬ 
sorption. 
CONCLUSION 
The results of these studies show that 
when western yellow pine is to be 
field planted in the northern Rocky 
Mountain region it is much better to 
use stock resulting from spring sow¬ 
ings for fall planting, but when spring 
planting is done it makes very little 
difference whether spring-sown or fall- 
sown stock be used. 
When spring sowing is practiced, it 
should be as early in the spring as 
possible. 
Fall sowing, if used, should be be¬ 
tween September 7 and October 15. 
Both seasons of sowing have definite 
advantages, but, all considered, spring 
seems to be the safest season as a gen¬ 
eral policy. Furthermore, spring sow¬ 
ing dovetails well with the general 
nursery work when there is a large 
amount of western white pine seed to 
be sown in the fall. 
4 From Oct. 21 to 27, 1918, at a depth of 5 inches on the site used, the daily maximum soil temperature 
averaged 42.0° and the daily minimum 38° F. 
