SEED PRODUCTION OF WESTERN WHITE PINE. 3 



sideration in determining the amount of seed production. Thus, 

 in measuring the seed crop, three things must be determined: (1) 

 The seed production for the stand per unit of area (not for individual 

 trees), (2) the quantity of seed, and (3) viability of the seed. The 

 weight of germinable seed per unit of area must be accepted as the 

 standard for measuring seed crops. If a is the weight of clean air- 

 dried seed obtained from 1 acre, and p is their germination per cent, 

 then the seed crop, or x, may be expressed by the formula x = ap. 



Since the aim is to determine the amount of seed produced per unit 

 of area, the best method of studying seed production is by means of 

 sample areas. These areas may be from one-quarter of an acre to 

 one-half of an acre in extent, in accordance with the density of the 

 stand. Each sample area, however, should include at least 100 trees 

 of the principal species composing the stand. 



It would, of course, be more accurate to gather cones and obtain 

 the seed from all of the trees on the sample area. This, however, 

 would necessitate the cutting down of the trees, which is not always 

 practicable or possible. Moreover, this operation would require a 

 great deal of time, which would make such an investigation difficult. 

 For this reason it is preferable to collect the cones and extract the 

 seed only from sample trees. 



It is a well-established fact that light is a necessary condition for 

 seed production, and observations show that the greater the amount 

 of light received by the tree the greater is its crown development and 

 the amount of seed produced. It may be already accepted a priori 

 that individual trees in a stand do not produce equal amounts of seed, 

 but vary in accordance with their crown development. In the 

 selection of the sample trees, therefore, one must be guided by the 

 form and blevelopment of the crown of the individual tree. In the 

 different species the different parts of the crown have varying im- 

 portance; thus in Douglas fir the upper part of the crown is of the 

 most importance, since it is there that the largest number of cones 

 are developed; in other species it may be the extremities of the 

 largest lower branches. 



In order that the amount of seed obtained from the sample trees 

 should, when multiplied by the total number of trees on the sample 

 plot, actually represent the amount of seed produced on the plot, 

 the sample trees must include representatives of all groups of trees 

 which differ in any way in their crown development. With this end 

 in view, all the trees on the sample plot are divided into groups in 

 accordance with their crown development, and their diameters 

 tallied. From these groups the sample trees are selected. As a basis 

 for dividing the trees into groups in accordance with their crown de- 

 velopment, the ordinary classification into dominant (I), codominant 



