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. 



Biittner (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). Neger and Biittner (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), Neger (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 Neger and Biittner, 

 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. Neger and Biittner 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 nurserymen 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 



