546 Journal of Agricultural Research voI.xv.no. 10 



what is their importance as compared with the parasites belonging to other 

 genera, under natural soil conditions. 



TRICHODERMA. 



Strains of Trichoderma frequently appear in cultures from seedlings 

 affected with the usual type of damping-off. They also often fruit on 

 the surface of recently autoclaved soil, entirely independently of the 

 presence of seedlings. Strains isolated at a Kansas nursery produced 

 conidiophores in very compact groups, often as much as 2 mm. in diame- 

 ter, and usually arranged in zonate rings. The spores were mostly 

 spherical. This agrees with the characters given for T. lignorum (Tode) 

 Harz., though one of the zonate strains isolated had the elliptical spores 

 described by Cook and Taubenhaus (5) for T. koningi Oudemans, and 

 another, with spherical or nearly spherical spores, showed the absence 

 of zonate spore-tuft production attributed to T. koningi. Frequent 

 chlamydospore formation, described as characteristic of T. koningi, was 

 observed in some of the strains whose isolation was not attempted. It 

 appears that both species, if they are to be regarded as distinct species, 

 are more or less common in pine seed beds. 



In an early inoculation test with an unidentified strain of Tricho- 

 derma from Washington, D. C, an autoclaved flat was sown with jack 

 pine, inoculated broadcast, and kept under moist-chamber conditions 

 without result. In a later experiment (No. 31, Table II) with the ellip- 

 tical-spored strain above referred to, the nonzonate strain, and the more 

 typical Trichoderma lignorum strain, in cultures of uncertain purity, 

 were used in heavy inoculation on five pots each with actually less para- 

 sitism than occurred in the controls. A fourth culture of Trichoderma sp. 

 of doubtful purity resulted in somewhat increased damping-off, but 

 within the limit of experimental error. 



In the experiment on sand treated with acid and lime, referred to in 

 the accounts of experiments with the preceding fungi, one pure and two 

 doubtfully pure cultures representing the three different types were 

 tested. The most typical strain of Trichoderma lignorum had no effect 

 on western yellow pine and little or none on jack pine. The nonzonate • 

 form and the elliptical-spored form both appeared to decrease germina- 

 tion in both pines, the former also increasing damping-off in western 

 yellow pine and the latter in jack pine. The differences were in all cases 

 within the limits of accidental variation. The indications from these 

 tests are that the strains of Trichoderma used are either unable to cause 

 the usual type of damping-off or are very unimportant causes. The 

 frequency with which the fungus is obtained in planted-plate cultures 

 from dead seedlings may easily be due to its common presence in soil 

 and its capacity for rapid growth on the agar used. 



In addition to the usual type of damping-off, the blacktop type, men- 

 tioned in the first part of the paper and illustrated in Plate B, figures 2 and 



