524 Journal of Agricultural Research voi. xv, no. io 



the seedlings affected by late damping-off are killed by the parasites. 

 Many of them, as in the case of the "root-sick" sugar-beet seedlings 

 described by Edson (7), have only the youngest portions of their roots 

 killed, and are able then to resist further attack, and so recover. Pine 

 seedlings on the margins of damped-off areas can be found at the age of 

 6 to 7 weeks, with more than half of their root systems decayed, but 

 with the older parts of the root intact and with vigorous laterals starting 

 from the terminal of the healthy portion. That such seedlings are 

 capable of recovery was demonstrated by replanting a number of badly 

 injured specimens of Corsican pine (Pimis nigra poiretianaY and observ- 

 ing their growth during the subsequent weeks. 



Pines affected with the late type of damping-oft' show no external 

 evidence of disease until they are practically dead. Infected seedlings 

 which recover do not, like the root-sick sugar beets described by Edson, 

 exhibit noticeably arrested growth and a flabby appearance of the tops. 



DAMPING-OFF OF TOPS 



A type of damping-off involving parts of the cotyledons or the upper 

 stem, while the lower stem and root remain sound until after the death 

 of the parts above, is fairly common under moist atmospheric condi- 

 tions, as in greenhouses, although seldom as prevalent in open seed beds 

 as the normal type of damping-off in which the root or the stem at the 

 ground line is first attacked. Infections are believed in the main to be 

 due to Fusarium. Under extremely moist conditions the mycelium 

 may spread directly to the other seedlings whose cotyledons touch the 

 diseased plant. Soil disinfection is, as would be expected, of relatively 

 little value in preventing this disease of the tops. Avoidance of exces- 

 sive atmospheric humidity appears especially important for control of 

 this type. 



A special case of damping-off of tops of seedlings is found in cases 

 in which the tips of all the cotyledons are simultaneously killed. This 

 at first suggests insufficient water supply as the cause, but examina- 

 tion of younger seedlings shows it to be parasitic. Infection occurs in 

 such cases while all the tips are still inclosed in the persistent seed coat. 

 This type of damping-off is thought to be caused most commonly by 

 species of Eusarium, but it has been observed in pots whose soil had 

 been inoculated with Corticium vagum, though absent in parallel control 

 pots. It is also possible that Pytliium debaryanum may be a cause of 

 this type, as there is abundant opportunity for infection to occur before 

 the tips of the cotyledons and the seed coat they carry are released from 

 the soil. Soil disinfection has apparently decreased losses from this type 

 of damping-off. 



1 The nomenclature used in this paper for foreign trees follows Bailey, L. H. standard cyclopedia 

 OP HORTICULTURE. New York, 1916; and for native trees follows George B. Sudworth in various 

 publications of the Forest Service, United States Department of Agriculture. 



