DAMPING-OFF IN FOREST NURSERIES. 89 



made. The strain available is much less destructive to the- pines 

 than most of the P. debaryanum strains used, and as the fungus has 

 never been isolated from coniferous seed beds it is not believed to 

 be of any great importance in forest nurseries. 



(10) Phytophthora sp. from Pinus resinosa seedlings has been suc- 

 cessfully used in inoculation on Pinus resinosa and in a preliminary 

 test on P. ponderosa. The strains available have been less destruc- 

 tive to the pines than Pythium debaryanum and the stronger strains 

 of Corticium vagum. It is not common. Its relation to Phytoph- 

 thora, fagi, the European damping-off parasite of both conifers and 

 dicotyledons, which has not been reported in this country, is being 

 investigated. 



(11) A fungus referred to Pythmrn artotrogus, also obtained from 

 damped-off Pinus resinosa, has indicated a very low degree of par- 

 asitism on this host, even less than that shown by the Rheospor- 

 angium and Phytophthora strains. An addition is made to the 

 statements in a previous paper concerning the ability of Botrytis 

 cinerea to cause damping-off in conifers. 



(12) The results of the cultural or direct examination of 742 dis- 

 ease foci in seed beds of various conifers are reported. Pythium, 

 debaryanum in the plate-culture examination method, considered 

 more reliable than direct examination, appeared in 51 per cent of 

 the foci from untreated beds, while Corticium vagum was found in 

 19 per cent. In foci in beds treated with various disinfectants, P. 

 debaryanum was* identified in 38 per cent of the foci and C. vagum 

 in only 4 per cent. When direct microscopic examination was sub- 

 stituted for isolation, C. vagum was found on a larger proportion 

 of the seedlings. It was not found at all in soil which had been 

 heated. The relative ease with which it appears to be controlled by 

 soil disinfection is in agreement with its poor adaptation for aerial 

 distribution. It was found more commonly in cases in which the 

 seedlings were directly examined than when cultures were made. 

 In view of the fact that at least some of the Corticium foci extend 

 rapidly and include very large numbers of seedlings, it seems that 

 the Corticium may be as important as P. debaryanum in causing the 

 damping-off of pines. 



(13) Fusarium spp. have occurred more commonly in plate cul- 

 tures than' either of the above-mentioned fungi. Because little is 

 known as to the parasitism of different species of this group on 

 conifers, it is not possible to make any statement regarding the im- 

 portance of the individual species. The evidence as a whole indi- 

 cates so much importance for Pythium debaryanum, Corticium 

 vagum, and for the Fusarium spp. considered as a group that no one 

 of the three can be safely said to be more important than the others* 

 Xone of the other fungi considered appear to be of real economic 

 rank in the United States. 



