June 3, 1933 
Snow Molding in Coniferous Nursery Stock 
743 
was found to be a notable exception. During the winter of 1919-1920 
a bed of some 300 vigorous 4-year-old jack pine transplants, 18 inches 
tall, was completely killed by the disease. Tables I and II clearly 
show that the Pacific Coast form of western yellow pine (Pinus pon- 
derosa), grown from seed collected in central Idaho, is much more sus¬ 
ceptible to the snow-molding fungi than the Rocky Mountain variety 
of the same species (Pinus ponderosa scoptUorum) ^ grown from seed 
collected in the region near the nursery. 
Tabi^E II .—Percentage of injury by snow-molding fungi in the several species and age 
classes, spring of ig 2 i 
Species. 
Age class. 
Bead. 
Alive but 
injured. 
Per cent. 
Per cent. 
Picea engelmanni . 
3--0 
8.4 
13-3 
3-1 
0, 8 
6.3 
3-2 
0 
3-4 
Picea excelsa . 
3-0 
80, 4 
II. 7 
3-3 
80.3 
19. 6 
Picea parryana . 
3-0 
60. 2 
30.8 
3-3 
3.0 
31* 5 
Pseudotsuga taxifolia .. 
i-o 
5-1 
6.9 
2-0 
16. 2 
19*3 
a 3-0 
2. 0 
5*4 
63-0 
31-1 
30*4 
Pinus ponderosa . 
i-o 
“•5 
3*5 
3 ~o 
0 
83. 0 
2-1 
37-2 
38.0 
2-2 
36.8 
35- 6 
Pinus ponderosa scopulorum ... 
1-0 
0.8 
I. 6 
3-0 
4-5 
18.5 
2-1 
23-7 
26.8 
2-2 
6.3 
24. 7 
Pinus contorta . 
2-1 
0 
3*0 
2-2 
0 
I* 5 
Abies concolor . 
3 “^ 
22. I 
30*8 
Pinus resinosa . 
2—1 
0 
15*8 
Pinus slrobus ... 
2-1 
60. 2 
39 * S 
Libocedrus decurrens . 
4. I 
8.4 
Thuja occidentalis . 
*T* 
100. 0 
0 
Juniperus monosperma . 
100. 0 
0 
a Bed protected by framework of 2 by 6 lumber. ^ Unprotected bed. 
Since most fungi will gain a foothold more readily at some previously 
injured part of a plant, it seems quite probable that the fungous injury 
during Ae winter of 1919-1920 was greatly increased as a result of the 
severe injury to the ends of the twigs by frost in the spring of 1919.^ 
In the spring of 1918 the problem of working out an efficacious method 
of controlling the snow molding of coniferous nursery stock was taken 
up by the writer. Six 4 by 12 foot beds were sown to the same amounts 
of Douglas fir, the time and method of sowing and subsequent care 
throughout the summer season being the same. Uniformly good stands 
were secured on all of the beds. The seed beds were covered with shade 
frames giving half shade during the hot, dry portion of the summer. 
In the autumn the shade frames were removed and just before the 
< Korstian, Clarence F. RypRcr a i,ats spring frost upon forrst vbgbtation in the wasatch 
MOUNTAINS OF UTAH. In Ecology, v. 2, p. 47-sa. i fig- 1921- Iriterature cited, p. 52. 
