12 BULLETIN 210, U. S. DEPARTMENT OF AGRICULTURE. 
TaBLe 5.—Distribution of the seed crop of western white pine, by crown classes. 
Ratios of seed production of crown classes.1 
Class I. | Class II. | Class III.| Class TV.| Class V. | Total. 
_—[——_—_— | 
Plot No. 1. 
Petal -vyield--<22...222-.- 2s. = per cent... 59.1 39.7 1,2 0 0 100 
Number. Of tE0S 26 is---5ae 2-2 oA do... 30 30 12 17 il 100 
Plot No. 2 
rrotaleyieldey sons oe I es ee cs Goss. 59.5 37.6 2.9 0 100 
Number of trees... ..¢2-2bs2—.. 2225 do.... 15 20 15 24 26 100 
Plot No. 8 
Motaleyield= seen = ce eee do:-=: 30.9 66.0 3.1 0 0 100 
Numperioftrees 4222-2. = |= sss: doi-s4 10 23 18 35 14 100 
Plot No. 4. 
Bieralwanlet feeee S02 2.28 3k eg qos "ee itse 4958 50.5 0.2 0 0 100 
Number oftrees.......--......-2g22 do:_2- 8 37 34 12 9 100 
PUUPIHP Ose mon oles feos oh eee 54.3 44.5 1.2 0 0 100 
5 27 1 22 15 100 
_ 1 Expressed in percentage of seed produced in each crown class of the plot divided by percentage of trees 
in the crown class. 
The ratios of productivity of trees of different crown classes in 
round figures are 3.5, 1.5, 0.05, 0.0. Thus a tree of crown Class I 
bears 70 times and a tree of crown Class II 30 times more seed than _ 
a tree of Class III. 25 
The participation of the different crown classes in the production 
of seed may serve as an index of the seed crop. In exceptionally 
good seed years not only the dominant classes bear seed, but even 
the oppressed trees have occasional cones, while in poor seed years 
cones are to be found only in the dominant class (1), and even then 
not on all trees or parts of their crowns. Between these two ex- 
tremes range seed crops of various abundance. The abundance 
of the seed crop can, therefore, be prognosticated very early in the © 
summer by observing in the forest the kind of trees that bear cones. 
In order to establish a regular yield for the seed production of western 
white pine, it would be necessary accurately to measure the crop — 
by the method described over several seed years of various intensity. 
After the seed production for the poorest, moderate, and excep- 
tionally good seed years is ascertained, the determination of whether 
the crop of a given year is good, fair, or poor can then be forecasted _ 
easily and early by merely observing the different crown classes of 
trees that are bearing cones. 
An attempt to penetrate deeper into the causes that determine — 
the average amount of seed produced by an individual tree of each 
crown class meets with difficulties because of the many counteracting 
factors, some of which still remain unexplained. Aside from the 
