Figure 6. — Open cones closed due to 

 moisture and hygroscopic swelling. 



B. Number of Seed Per Acre 



The number of cones per acre can be multiplied by an estimated number of seed per 

 cone to arrive at number of seed per acre for the area of interest. A direct seed 

 count from sample cones collected on or near the study plots is recommended. 



Although direct seed counts are apt to be more reliable, average cone length can 

 be used as a basis for estimating number of seed per cone. See Thompson's formula 

 (1969) presented below: 



Y = 10. 3X - 25.3 (3) 



where Y = Number of seed per cone, 



X = Cone length in cm. and X >_ 2.5 cm. 



But the r^ value (0.38) in Thompson's data was rather low, and there is no guarantee 

 against bias in application. 



C. Number of Viable Seed Per Acre 



Either cutting or germination tests should be conducted on seed from the sample 

 cones to obtain the percentage of viable seed; this value can then be multiplied by the 

 total seed estimated for the area to arrive at total viable seed. 



The viability of seed from serotinous cones varies substantially between areas and 

 from year to year (from 10 to 90 percent, in our experience). 



6 



