. [Bulletins on forest pathology : from Bulletin , Washington, , 1913-1925]. Trees; Plant diseases. 74 BULLETIN 934, U. S. DEPARTMENT OE AGRICULTURE. DENSITY OF SOWING. The relation between the disease and thick sowing was strikingly indicated for tobacco seedlings in a single experiment by Johnson (82). For pines the only available information is from four experi- ments on Pinus banksiana. The results of the first two appear in figure 19. In both experiments there is an indication of an increase in the percentage of diseased plants as the seed density is increased. There is, howev
. [Bulletins on forest pathology : from Bulletin , Washington, , 1913-1925]. Trees; Plant diseases. 74 BULLETIN 934, U. S. DEPARTMENT OE AGRICULTURE. DENSITY OF SOWING. The relation between the disease and thick sowing was strikingly indicated for tobacco seedlings in a single experiment by Johnson (82). For pines the only available information is from four experi- ments on Pinus banksiana. The results of the first two appear in figure 19. In both experiments there is an indication of an increase in the percentage of diseased plants as the seed density is increased. There is, however,\no such marked relation as in Johnson's work. As the pines were sown in drills, they were so close together even in the less dense plats that no very great increase in the ease of spread of the disease was to be expected from in- creasing the density. Greater differences should be expected in broadcast beds. That heavier losses have been found in drill-sown beds than in those sown broad- ly ^soh / cast (69? 139) is pre- / sumably explained by the fact that with equal numbers of seed per square foot of seed bed the seed- lings are much closer together in drills than in broadcast beds, and thus the spread of the mycelium of para- sites from one seedling to another is facilitated. Two tests of different seed densities were also made in 3-inch pots of autoclaved soil in the greenhouse. Each regular pot was sown with 28 seeds (equivalent to 600 per square foot). The pots were inoculated by adding to each a single small fragment of an agar culture of PytMum debaryanum. Uninoculated pots showed an emer- gence of approximately 50 per cent of the seed and were entirely free from subsequent damping-off in both experiments. The results ap- pear in Table XL In this case not only the damping-off after emergence but the loss before the seedlings appeared bore an apparent relation to sowing density. In the field experiments there was no evidence that the loss before the seedlings appeared
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