THE NATIONAL NURSERYMAN 
115 
Studies in Forest Tree Seeds! Relation Between Germination 
and Soil Moisture 
By Echo. N. Manns, Forest Examiner, U. S. Forest Service. 
^JVt'OR several years past llie elose correlation between 
£J I germination ol forest tree seeds and the factors 
necessary to germination has been made a sub¬ 
ject of study at the Converse Experiment Station of the 
U. S. Forest Service, in Southern California. Interest 
was amused in this matter by the widely differing per¬ 
centages of germination secured from the same lot of 
seed under field conditions. Ihese differences in ger¬ 
mination, amounting to as high as 50 per cent, could be 
accounted lor only through a difference in the external 
factors acting upon the seed. It is a matter of common 
knowledge that both maturity and dryness of seed are 
responsible for great differences in germination, and 
that often under the same treatment seeds of the same 
species will behave differently according to their age 
and degree of ripening. 
Water, moderately high temperatures, and oxygen are 
the chief essentials for the germination of all seeds, (he 
Western tellow Pine. 
Germination thr Cent by Days tor Carious Soil Moistures. 
Figure 1. 
influence of light in itself being more or less a negligible 
factor. In general, oxygen is a constant except under 
certain abnormal conditions, while temperature fluc¬ 
tuates in response to barometric and seasonal conditions 
beyond the control of man, leaving water as the one ele¬ 
ment which man can control to some extent in nursery 
practice. Boerker (1) lias shown for three “averaged” 
soil moistures that germination varied with the water 
content of the soil, but the range in values included 
“dry,” “medium wet,” and “wet” soils, with minimum 
soil moisture contents of 5.1, 11.8 and 23.9 per cent, 
respectively. It has been repeatedly noted by forest 
practitioners that a great difference in germination 
existed between the same lot of seed when grown in (he 
greenhouse and in the field. In fact it is common exper¬ 
ience of those in charge of nursery work to find such 
wide discrepancies in seed values between greenhouse 
tests and field practice that serious doubts are cast upon 
the practical value of these tests. 
Such discrepancies in actual practice gave rise to the 
belief that they could be controlled and perhaps elim¬ 
inated through the factors controlling germination. 
Equipment was not available to make an exhaustive 
study at first. Therefore to determine the value of the 
hypothesis, three small seed beds were sown in the nur¬ 
sery to western yellow pine (Finns ponderosa) in the 
spring ol 1915, and kept as close to a constant soil mois¬ 
ture as was possible. Soil samples were taken daily, 
and, by compacting the subsoil, reducing evaporation, 
and frequent waterings, moistures of 10, 15, and 20 per 
cent were maintained with slight variations. Germina¬ 
tions secured from these was 41 per cent, 78 per cent, 
and 93 per cent respectively, with marked differences as 
to the rate of germination. 
(1) Richard H. D. Boerker. Ecological Investigations upon the 
Germination and Early Growth of Forest Trees Univ of Ne¬ 
braska. 81 pp. 1916. 
Incense Cedar 
(jermmat/on f-br Cent of See d by So// /l/oisture Cor/en/s 
Figure 2, 
Two series of tests were run the following winter on 
yelow pine seed (F. ponderosa). The seeds were sown in 
cans in approximatey the same amount of sand, and 
coovered to an equal depth. By frequent weighings and 
the addition of water when necessary, the moisture 
content was kept, with very slight fluctuations, close to 
the desired per cent. By this means soil moistures of 
from 5 to 40 per cent at 5 per cent intervals were ob¬ 
tained. This resulted in germination values of 6, 38, 
95, 87, 69, 26, 3, 0 per cents, respectively, with large dif¬ 
ferences in the rates of germination. 
Since the first trials . were carried out, additional 
series have been run on jeffrey pine (F. jejfreyi ), mon- 
terey pine (P. radiata ), austrian pine (F. austriaca), 
scots pine ( P. sylvestris ), lodgepole pine (P. contorta ), 
incense cedar (Libocedrus decurrens ), and white fir 
(Abies concolor). Each series has been made in the 
same manner, though there has been a difference in the 
kind of sand used, the amount of sand per can, the 
amount and age of seed, the depth the seed has been cov¬ 
ered, and the temperatures. Apparently temperature af- 
lects the rate more than the total amount of germina- 
