10 BULLETIN 1200, U. S. DEPARTMENT OF AGRICULTURE. 
Soil may be largely responsible for limiting the distribution of a 
species, especially in local areas. Thus on the areas of serpentine 
in the Siskiyou Mountains of southwestern Oregon, knobcone pine 
produces a better growth during its seedling and pole stages than 
Douglas fir and takes possession of such shallow soil areas. 
Although the knobcone pine is only a scrub tree, the soil enables it 
to compete successfully with its associated timber trees, including 
the Douglas fir. 
The loose soil in the Coast and Cascade Mountain regions of 
Oregon and Washington affords good drainage, prevents erosion, 
and, with abundant rainfall, is very favorable to the growth of 
Douglas fir. 
SEED. 
The proposed methods of natural restocking of Douglas fir are 
in large part based on the characteristics of the seed and the stor- 
age of seed in the forest floor. In order to assure a stand of young 
growth after forest fires or logging, good crops of seed must be pro- 
duced, and the seed must be distributed and be able to retain its 
vitality until it has an opportunity to germinate. A study of 
the seed has established important facts concerning its produc- 
tion, distribution, germination, and viability—facts that must 
be clearly understood as the first step in solving the problem of 
natural regeneration of Douglas fir.’ 
SEED PRODUCTION. 
In the Douglas fir good seed years occur at irregular intervals, 
usually two or three years apart. Sometimes a fair crop of seed 
follows after a very heavy crop, and at other times practically no 
seed is produced in this region following a heavy seed year. Seed 
production is unquestionably influenced by the condition of the 
weather during the period of pollination. During seasons in which 
rains began at about the time the staminate flowers opened, and con- 
tinuous wet weather prevailed throughout the season of pollination, 
it was noted that the staminate flowers drooped, the pollen adhered 
to the stamens, and there was apparently very little distribution of 
the pollen. Even on trees that produced a good crop of pistillate 
flowers there were practically no cones. As the pistillate flowers 
are at the ends of the branches and the staminate flowers further 
down, there is very little pollination on the same branch, and the 
distribution of pollen to other branches is very hmited on account 
of its sticky condition. The wide variation of climatic conditions 
in mountainous regions causes a corresponding variation in the time 
of flowering. Although the staminate flowers on the same tree may 
mature before the pistillate, the trees at a higher elevation, in the 
same vicinity, may produce pollen at the proper time to fertilize the 
pistillate flowers of the trees in the valley. This cross-pollination 
tends to eliminate individuality among trees in the same locality, 
in so far as fertilization is concerned, although there are other 
factors affecting the development of the seed, such as soil and age 
of tree. 
The distribttion by-wind of the pollen of Douglas fir may cause 
cross-pollination for long distances during favorable periods. Pol- 
