NURSERY PRACTICE ON THE NATIONAL FORESTS. 
31 
Covering of the seed beds during the germination period is resorted 
to for other reasons than protection against rodents or birds. Chief 
among these is keeping the beds as uniformly moist as possible, 
which undoubtedly promotes the highest germination of the seed. 
Covering also eliminates the need of such frequent waterings as are 
necessary in uncovered beds. For the purpose of keeping the beds 
uniformly moist, the sides and ends of the wire frame just discussed 
are covered with building, tar, or wrapping paper, or burlap, and a 
lath shade frame is set on top of it. Burlap is better than paper 
because it is easier to handle, does not tear, and can be used for two 
successive years. The lath frame is constructed as shown in figure 
5. A complete shade or covering is obtained by laying a loose lath 
in each interspace between those which are nailed to the frame. 
Full or partial shade, without the side covering of burlap, is often 
given the beds by means of this lath frame, some other form of a 
low-shade frame, or high-shade frames with a slatting cover. 
TOP VIEW 
SIOE VIEW 
n n n n n n i 
X 
Fig. 5. — Pettis seed-bed frame. 
Recent experience has developed the fact that such shade coverings 
are neither necessary nor desirable in all nurseries where they have 
been used. This is especially true in the cooler and moister regions 
and with seed which germinates slowly. Heat as well as moisture is 
essential for germination of seed; and in moist seed beds tightly 
screened from the sun's rays, the temperature of the soil may be kept 
so low as to delay germination considerably. This happened with 
Douglas fir at the Wind River Nursery. Seed in seed beds without 
side or overhead cover, or with a cover of one thickness of burlap 
only, germinated twice as fast in the first month as those under the 
regular Pettis frames. At the Cottonwood, Pilgrim Creek, and 
