10 
BULLETIN 934, U. S. DEPARTMENT OE AGPJCEXT 1 
RE. 
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 
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■Akf- 
urn 
Fig. 4. — The beginning of an epidemic in drill-sown Pinus VanJesiana. 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 
Pi/thium debaryaruam (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. 
