52 BULLETIN 479, U. S. DEPARTMENT OF AGRICULTURE. 
with a 10-minute exposure, of 12 per cent with a 15-minute ex- 
posure, of 40 per cent with a 20-minute exposure, and of 90 per 
cent with a 4-hour exposure. While some stock survived even 
after 4 hours' exposure, it sustained in an increasing ratio a serious 
retardation in growth as the period of exposure increased. 
EOOT TKIMMING. 
After being removed from the seed beds the roots of seedlings may 
be trimmed or pruned to a length of 6 or 7 inches before they are 
transplanted. A sharp knife, scissors, hatchet, or meat ax is suit- 
able for the operation. Usually a bunch of seedlings are gathered in 
one hand and the roots of all pruned at the same time. In this 
operation special care should be taken to remove all badly skinned, 
broken, or diseased roots. 
Root trimming facilitates transplanting operations, because the 
trenches do not have to be dug deeply to receive the seedlings; and 
to some extent it promotes the formation of a compact, well-devel- 
oped root system. On the other hand, if it is carelessly done, the 
roots of some seedlings are likely to be cut so short as to injure them 
and cause greater losses in the transplant beds. Moreover, in dig- 
ging seedlings for transplating it is seldom, unless special care is 
taken, that roots longer than from 8 to 10 inches are retained. These 
are not too long for rapid and successful transplanting. At the 
Boulder Nursery the conclusion has been reached that with Douglas 
fir root pruning makes the stock less desirable for planting on areas 
east of the Continental Divide, because it induces the formation of a 
root system too superficial for best results in planting in this dry 
region. In general, where the seed-bed operations are properly car- 
ried out root priming is unnecessary. 
GKADING SEEDLINGS. 
Seedlings which are badly damaged in digging and those which 
have very poor root systems or poorly developed tops should not be 
transplanted. Their use makes certain a greater loss in the trans- 
plant beds and the production of a mixed quality of transplant stock, 
some of which at the end of the regular rotation for the species is 
too poorly developed for field planting. Such seedlings should be 
discarded or, at most, transplanted in beds separate from the better 
stock. The discarding or grading can be done either when the seed- 
lings are being removed from the seed beds or, better, as they are 
threaded into the transplant boards. In the latter case men with 
good judgment in this matter will have to be assigned to the thread- 
ing tables. The importance of discarding or grading out such stock 
justifies the operation being practiced at all nurseries. 
