14 BULLETIN 1200, U. S. DEPARTMENT OF AGRICULTURE. 
Seeds in the forest floor are often covered with deep layers of litter 
and duif, and when the forest is removed the conditions may be favor- | 
able for the germination of the seeds. If, however, the seeds are | 
buried too deeply the food in: the seed is not sufficient to enable the 
seedling to grow to the surface. The effect of depth of cover, and 
the superiority of the seedling which springs from a large seed, are 
shown in Table 4. : 
TABLE 4.—Effect of depth of cover on germination. 
| i I 
| 
1 Ap- H | : 
Depth | Gormi-| Pa Depth | _ | Ap- 
: ermi-| peared : Pt. | Germi-| 
BENE ee |nated. | above |) SE eS. anol nated. renawel 
| ground. |) | ground 
: _ Inches. | Per ct. | Per ct. | Inches.| Per ct. | Per ct 
Western yellow pine..... 1 82 | 82 || Western hemlock. ....... 0.25 | 96 
Leds 83 | 7 BS 92 | 7 
hs 71 | 2 75 86 50 
| 1.0. | 64 5 
“Douslaspfirs tess ose | a0 93 | 93 |, 1.25 | 42 | 0 
ua 87 85 || Western red cedar....___- (12) 7 7 
amelea 72 64 | 25| 64 52 
[sta 67 | 50 || ee eee © 24 
} 3 42 | 3 || | 15 | 25 4 
4 17 0 |; 1.0 } 26 0 
. 1.5 {19 | 0 
Table 4 shows that seedlings will come up through a depth of soil 
in direct proportion to the size of the seed, and the development of 
the seedlings proves that they will grow to a size directly propor- 
tional to the size of the seed without any nourishment other than that 
stored in the endosperm of the seed. The fact that the seeds germi- 
nated even at the depth shown in this table and produced roots some- 
times 4 to 5 inches long, as did the western yellow pine, shows that 
the seedling is nourished by food stored in the seed until it can pro- 
duce chlorophyll bodies and manufacture its own food. If it can not 
reach the surface before the supply of nourishment in the seed is ex- 
hausted, it must die. If the seedling is able to get above the ground, 
even as a final effort, the cotyledons open at once and turn green, and 
the seedling gets a new supply of food. 
The loss of many of the seedlings germinating in the shade is 
caused by disease and is due only indirectly to shading, because the 
shade and moisture favor the development of the damping-off fungi. 
This may account for more of the seedlings being found in the open, 
but it does not necessarily mean that the species involved will not 
develop under more shade. The amount of shading that seedlings 
will endure largely determines the understory and, consequently, the 
succession of species. Douglas-fir seedlings will not survive in as 
dense shade as will the seedlings of western hemlock and western red 
cedar. For this reason the latter species eventually gain possession 
of an area that remains undisturbed. iat 
SEED VIABILITY. 
Viability of seed is one of the most important factors in the imme- 
diate reproduction of the forest as well as in the retention of a forest 
type. When a forest -is destroyed by fire, wind, cutting, or other 
