10 



BULLETIN 034, 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 ~banKs{ann . 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 

 Pythium 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 investigation. 



