FOREST TREE SEED AND SEED COLLECTING 129 



tive energy period of Douglas fir for Wyoming use at 35 days and 

 for Colorado use at 21 days. After many tests made in the hot- 

 house, he accepted 25 days as the energy period for western yellow 

 pine, 22 days for Engelmann spruce, and 31 days for lodgepole pine 

 for use in the northern Rocky Mountain region. From a series of 

 experiments conducted by Zederbauer, 1 he concludes that from 14 

 to 21 days are sufficient for most conifers. Tests made by him on 

 clay plates under a day temperature of from 71 to 73 F. lowered 

 to 60 F. at night, and others made on filter paper in a germinating 

 oven at a constant temperature of 73 F. gave the following 

 germinative energy periods: 



Days. Days. 



White pine 30-40 Douglas fir 28 



Lodgepole pine. ... 28 Western hemlock 21 



Pitch pine 14 Western red cedar 21 



Jack pine 14 Bigtree 14-21 



Blue spruce 14 Chamaecyparis (various 



Black spruce 21 species) 21 



Sitka spruce 21 



In 1907, the officials of various seed-testing stations, at the 

 International Congress for Agriculture and Forestry held at 

 Vienna, agreed that germination tests conducted under the most 

 favorable conditions should be concluded after a set time as 

 shown below. 



Days. 



European larch, nearly all pines and various species of Chamaecyparis 20 



Scotch pine 30 



White pine 60 



Alder and birch 20 



Most other broadleaved species 30 



In the author's opinion, figures showing the course of germination, 

 i.e., the germination in 5, 10, 20, 30, 60, and 100 days, are more 

 useful than those showing germinative energy. When the full 

 data showing the course of germination of a given species is 

 available, judgment as to how long a test should continue can be 

 more satisfactorily determined. Rafn's 2 researches show the aver- 

 age course of germination for a large number of American species 

 to be as follows : 



1 Zederbauer, E.: Die Keimpriifungsdauer einiger Koniferen. (Centralblatt 

 f. d. gesamte Forstwesen, S. 306-313. 1906.) 



2 Rafn, Johannes: The testing of forest seeds during 25 years. (Printed 

 by the author for private circulation.) 1915. 



