DAMPING-OFF IN FOREST NURSERIES. 19 
which the disease is either accidentally absent or is artifically con- 
trolled. Such an experiment is within the silvical rather than the 
pathological investigative field. If it be found that there is some 
selective value in the action of the disease and that it is greater in 
untreated than in treated beds, it would still seem that a much more 
desirable and dependable selection could be obtained by discarding 
weak plants at the time of transplanting than by letting damping- 
off run uncontrolled in the seed beds. Damping-off is sometimes 
negligible and sometimes destroys practically all the seedlings in a 
given area, in neither of which cases can it have any material selective 
value. 
RELATIVE SUSCEPTIBILITY OF DIFFERENT CONIFERS. 
Buttner ('25) writing of European conditions, states that exotic 
conifers are especially subject to damping-off. He includes fir, 
spruce, pines, larches, and cypress in this statement. He mentions 
the same subject in a later paper (26). Xeger and Buttner (91) give 
a long list of different species of conifers from various parts of the 
world with statements as to their susceptibility to damping-off. 
Beissner (11, p. 656-657), Xeger (93), Clinton (28), Bates and 
Pierce (7), Boerker (13), and Tillotson (139, p. 69) have all given 
information on the susceptibility of different conifers. The data re- 
ported by Tillotson are drawn from reports by various officers of the 
United States Forest Service which he has compiled. While it is 
probable that the nurserymen who are responsible for most of his 
records have not observed the disease as closely as Xeger and Buttner, 
the fact that their observations are mostly based on repeated seasons' 
work with large-scale seed beds of the species they report on makes 
their observations in some respects more reliable than the other pub- 
lished data. Xeger and Buttner presumably worked in most cases 
with small beds of the various conifers on which they report, and the 
variations which they attribute to differences in specific resistance 
might easily in such case be largely due to accidental variation. The 
error which nurserj-men are most likely to make in their notes on 
susceptibility is to underestimate the loss, especially for the small- 
seeded species. The seedlings of small-seeded conifers decay and 
shrivel so quickly after they fall that in taking notes at any one time 
only a small proportion of the total loss is visible. Frequent counts 
of dead. seedlings are the only way by which the loss after germina- 
tion in such species can be properly appreciated. 
The data given by the authors mentioned in the foregoing para- 
graph, together with unpublished data obtained by personal observa- 
tion or from commercial and other nurserymen in the United States, 
are summarized in Table II, the source of each report being shown 
by letters signifying the authority. The unpublished data on two 
