2 BULLETIN 210, U. S. DEPARTMENT OF AGRICULTURE. 
taking as it seems. Should the seed crop be estimated ocularly or 
actually measured on representative trees or sample plots? If it is 
to be measured, what is to be taken as the unit of measure—the 
number of cones produced by a few individual trees, the number of — | 
cones produced per unit of area, or the quantity of germinable seed | 
produced by individual trees on a given area? 
When a method is agreed upon, the problem of the periodicity of | 
seed crops can be attacked. To solve this problem, repeated com-— 
parable investigations of the first problem carried on for years is 
necessary. 
In the solution of the third problem there enters the determination, 
first, of the external factors such as climate, soil, exposure, light, ~ 
injury, and destruction of seed by animals and fungi, and, second, of — 
internal factors, such as composition, age, density, and health of the — 
stand. The solution of this complicated question, or rather of this 
series of complicated questions, requires systematic, parallel, and — 
uninterrupted series of investigations, which can not be undertaken by 
one individual, but must be carried on by permanently organized 
- forest experiment stations. 
The fourth problem, the solution of which is the final aim of the 
whole investigation, is the most difficult of all, and requires, in addi- — 
tion to the other lines of work, a series of chemical, physiological, and 
anatomical investigations. 
In this paper an attempt will be made to discuss merely the method | 
of measuring seed crops. 
METHOD EMPLOYED IN MEASURING THE SEED CROP. 
The production of seed in forest trees is not a function of an indi- 
vidual tree, but really of the whole stand, since the development of © 
the life processes of each tree is determined by the density, composi- 
tion, and age of the stand, and by the position of the tree in the stand. 
Therefore, in determining the amount of the seed crop, the quantity 
of seed produced per unit of area, and not the amount produced by 
individual trees, should be made the basis of measurement. Further, 
the cone production can not alone serve as a basis for measuring the | 
seed crop. The seed production must be measured not by the quan- 
tity of cones but by the amount of seed produced, because the 
final aim in the study of seed crops is not the cones but the seed. — 
The quality of seed, therefore, viz, its viability, must be taken into ~ 
account. Two stands may produce different quantities of cones per 
tree, yet the stand with the smaller average number of cones per tree F | 
may furnish more germinable seed than the stand with the larger | 
number of cones. Barren seed are biologically nothing but impuri- — 
ties, and it would therefore be a mistake not to leave them out of con- | 
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