. [Bulletins on forest pathology : from Bulletin , Washington, , 1913-1925]. Trees; Plant diseases. 10 BULLETIN" 934, U. S. DEPARTMENT OF AGRICULTURE. observing their continued growth (fig. 6). An article recently found (25) shows that Biittner had earlier made the same sort of demonstration of recovery of root-sick conifers. Observations on olive seedlings in 1916 showed cases of partially rotted roots which were recovering by sending out lateral root branches. (4) Top damping: The cotyledons or upper part of the stem are invaded by the parasite, sometimes before the seedling
. [Bulletins on forest pathology : from Bulletin , Washington, , 1913-1925]. Trees; Plant diseases. 10 BULLETIN" 934, U. S. DEPARTMENT OF AGRICULTURE. observing their continued growth (fig. 6). An article recently found (25) shows that Biittner had earlier made the same sort of demonstration of recovery of root-sick conifers. Observations on olive seedlings in 1916 showed cases of partially rotted roots which were recovering by sending out lateral root branches. (4) Top damping: The cotyledons or upper part of the stem are invaded by the parasite, sometimes before the seedling breaks through the soil. The infec- tion may or may not be fatal. A special case of this type, probably caused by a different parasite from those most commonly active, is that which in a publica- tion above referred to was described and figured as " black-top " (68). It is. Fig. 4.—The beginning of an epidemic in drill-sown Pinus hanksiann, Black crosses (X) indicate disease foci where the germinating seed were apparently killed and from which the disease is now spreading to adjacent seedlings. (Photographed by Dr. J. V. Hofmann.) distinguished from ordinary top damping by the very dark color of the invaded tissues and its apparent dependence on some unusual set of climatic factors for its progress in the seedling after infection. The killing of dormant seed by fungi is a matter of some practical interest in seed beds, and possibly still more so in forests, as it may help to explain the failure of certain conifers to reproduce except on mineral or certain other special soil types (68). With sugar beets Pythiwn debaryanum (100) is said to attack dormant seed as well as seeds which have sprouted. It is to be presumed that with conifers some of the damping-off fungi will be found to attack dormant as well as sprouting seed. This matter is now under Please note that these images are extracted from scanned page images that may have been digitally enhance
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