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



satisfactory, though the acid treatment has now been in successful 

 use for several years at some nurseries. At most nurseries, if the 

 minimum effective quantity of acid is used, there is no need of any 

 special precautions to prevent injury to the seedlings. It is not 

 expected that any single treatment can be found that can be uni- 

 versally applied without change in details irrespective of differences 

 in soil characters and in fungous flora. 



(7) Corticiwm vagum and Fusarium spp. have been previously 

 shown to be parasitic on pine seedlings. Different strains of 0. 

 vagum are found to vary considerably in their ability to cause damp- 

 ing-off, certain strains being consistently destructive and others 

 much less active in tests conducted on different species of pine and 

 several years apart. The differences in activity between strains 

 were greater, and apparently rather more constant from one ex- 

 periment to the next, than with Peltier's strains in his carnation ex- 

 periments. Comparison of the results on pine with those of Edson 

 and Shapovalov on potato gives some indication that strains vigor- 

 ously parasitic on one of these hosts are likely to be parasitic on the 

 other also. 



(8) Pythium debaryanum^ reported on many hosts and proved to 

 be parasitic on few, is shown by repeated inoculation, reisolation, 

 and reinoculation.to be capable of causing the damping-off of seed- 

 lings of pine species. The identity qf the fungus causing the damp- 

 ing-off of conifers with that attacking dicotyledons has been estab- 

 lished by cross-inoculations as > well as by morphological comparison. 

 Inoculations on unheated soil are much less destructive than on 

 heated soil. Pythium debaryanum has been obtained in culture from 

 Picea engelmanni, P. sitchensis, Tsuga mertensiana, Pinus banksiana, 

 P. nigra austriaca, P. ponderosa, P. resinosa, and Pseudotsuga taxi- 

 folia. In addition, fenugreek (Trigonella foenum-graecum) , cowpea 

 (Vigna sp.), and rice (Oryza sativa) are reported as apparently new 

 hosts among the dicotyledons. In inoculations the fungus has been 

 successfully used on Pinus banksiana, P. ponderosa, P. resinosa, and 

 in a preliminary experiment on Pseudotsuga taxifolia. It had 

 already been successfully used in preliminary inoculations on Picea 

 canadensis by Hofmann (77). 



Differences in parasitic activity on pine are found between differ- 

 ent strains of Pythium debaryanum. These differences are not as 

 large and partly for this reason their constancy is not quite as con- 

 clusively demonstrated as in the case of the strains of Corticium 

 vagum. 



(9) Rheosporangium aplianidermatus Edson, a parasite of radish 

 and sugar beet, in many ways closely resembling Pythium debary- 

 anum, has killed seedlings of Pinus lanksiana and P. resinosa in 

 certain experiments, and reisolations and reinoculations have been 



