66 BULLETIN 934, U. S. DEPARTMENT OF AGRICULTURE. 



For the conifers, no very reliable data on relative importance have 

 been published. Numerous European reports emphasize the damage 

 due to Fusarium spp., while a smaller number attribute loss to 

 Phytophthora fagi or to both. There seems to have been little effort 

 to determine the presence or absence of Corticium or Pythium, so 

 these reports can not be given great weight. Spaulding's evident 

 belief (136) in the importance of Fusarium has more weight, as he 

 was on the lookout for the other fungi ; the moist-chamber diagnostic 

 method employed in most . of this work was, however, not well 

 adapted to the detection of either one. The same is true of the work 

 of Rathbun (106), in which dilution plates of seed-bed soil were 

 employed. Rankin (105) attributes to Fusarium spp. the greatest 

 importance in tree seed beds in this country, with Pythium debary- 

 anum and Rhizoctonia spp. important in certain cases. Gifford (46) 

 emphasizes the importance of Fusarium, while Clinton (28) appar- 

 ently found Rhizoctonia (Corticium vagum) especially prevalent 

 in the examinations he made. 



On the basis of the data presented or summarized in this bulletin, 

 it is believed that of the various organisms which have been con- 

 nected with damping-off in coniferous seed beds Pythium debary- 

 aimm, Corticium vagum, and Fusarium spp. include all of impor- 

 tance. The others, either because of low indicated virulence or 

 infrequent occurrence, and in most cases both, do not seem to merit 

 extensive consideration. 



In order to form an idea of the relative frequency of the parasites 

 named above as important, there have been brought together in 

 Table IX the results of the examination of 438 damping-off foci in 

 untreated beds and 304 foci which have appeared in beds which had 

 received various disinfectant treatments. The data are presented 

 by foci rather than by individual seedlings, as was done in the census 

 reported by Busse and his coworkers. Most of the diagnoses were 

 made by planting recently diseased seedlings in plates of solidified 

 prune agar, all the seedlings taken from the same "focus, or " patch," 

 of damped- off seedlings being put into the same Petri dish. The 

 resulting growth was in some cases transferred to a tube for later 

 examination,, but was usually examined directly in the plate. In a 

 smaller number of foci the seedlings were macerated and examined 

 directly without recourse to culture methods. As Pythium debary- 

 anum does not commonly fruit in diseased seedlings of pine or of 

 tobacco (81) and its hyphse are both difficult to find and not in 

 themselves considered a sufficient diagnostic character, this latter 

 method of examination is not so satisfactory for the determination of 

 Pythium as it is for Corticium, which is easily recognized by its 



