NURSERY PRACTICE ON THE NATIONAL FORESTS. 29 
red pine, to three-eighth inch with larger seed, such as white pine, 
Douglas fir, western yellow pine, and Jeffrey pine. Germination is 
better and more uniform, and at the Bessey and Savenac nurseries 
damping-off is less severe in shallow than in deeply covered beds. 
A loose, friable soil, such as sand or a mixture of sand and loam, 
makes the best cover. A cover of sand gives quicker and more uni- 
form germination than any other; it can be put through a screen 
more easily ; it retards evaporation excellently, more effectually pre- 
vents caking of the surface and the lifting of cakes bodily by the 
germinating seed; it decreases the danger of damping-off, and it 
gradually improves the texture of a heavier underlying soil. Fur- 
thermore, moss is less likely to form on a sandy than on a loamy 
surface. 
COVERING OF THE SEED BEDS. 
After sowing and covering the seed there is, at some nurseries, an 
advantage in covering the seed beds. Protection of the seed against 
rodents, particularly mice and chipmunks, and of the seedlings 
(when they first appear above the surface of the soil with the seed 
coat attached) against birds is very often necessary. A common and 
effective means of protection is a screened frame cover of the same 
size as the seed beds, ordinarily 4 by 12 feet, the bottom sill sunk 
into the soil around the seed bed, and the top high enough above the 
bed so as not to interfere with the development of the seedlings. 
The top is removable to permit weeding. Such a frame, called a 
" Pettis frame," is described in Forest Service Bulletin 76, and the 
drawings are reproduced here (fig. 4). 
A modified type of this frame is used at the Wind River Nursery. 
The corner and side posts project an inch above the top plate in 
order to hold the cover in place on the frame. Further, the sides 
and ends are constructed separately and the frames afterwards set 
up. This method of construction results in two posts at each corner, 
one of which fits in front of the other. The frame is set up by 
bolting the two corner posts together or simply by inserting a large 
20d. nail in the hole bored for the bolt. The principal merit of 
this is that the frames can be quickly taken apart and when stored 
require much less space. 
Before construction the framework material should be painted to 
preserve the frames and improve their appearance. Experiments at 
the Wind River Nursery indicate that a light grade of creosote ap- 
plied to the lower sill of the seed-bed frame will not harm Douglas 
fir seedlings if not more than two coats are given. Carbolineum of 
the grade used proved unsatisfactory. Both of these preservatives 
vary so much in grades that in general it is unsafe to use them 
unless they have been proved satisfactory by experiment. 
