526 Journal of Agricultural Research ^i-oi. xv. no. lo 



In cases of conifers which fail to reproduce well in forest soils contain- 

 ing much humus or covered with litter, the possibilities of parasitic 

 germination loss or of the decay of seed before germination starts are 

 to be considered. In stands of scrub pine {Pinus virginiana) , loblolly 

 pine (P. iaeda), shortleaf pine (P. echinata), and pitch pine (P. rigida) 

 in the vicinity of Washington, D. C, where recently germinated seed- 

 lings on bare mineral soils are numerous, search failed to show either 

 seedlings or germinating seed in the litter at points where mineral soil 

 was not exposed. As sufficient moisture was present in the upper 

 layers of the litter, and seed of broad-leaved species was found germi- 

 nating in fair quantity, suspicion is directed toward some biologic factor 

 as the cause of the lack of conifers. It is suggested that the decay of 

 dormant seed by the vigorous, ordinarily saprophytic mycelia present 

 in leaf mold may prove an important cause of failure to secure natural 

 reproduction of some conifers on humus soils. The entire matter of 

 the importance of the different types of damping-off in limiting reproduc- 

 tion in coniferous forests needs investigation. 



INOCULATION PROCEDURE; 

 STANDARD INOCULATION METHOD 



Except where otherwise stated, all of the experiments whose' results 

 appear in this paper were conducted by the following methods: 



Inoculum was added to the soil on which the seed was sown, instead 

 of appl5dng it directly to the seedlings themselves. The procedure 

 was to sow the seed broadcast in pots of a mixture of sand and loam, 

 in most cases containing some compost. The pots and contained soil 

 were sterilized by steam pressure one to three days before seed sowing. 

 The inoculum v/as laid on the soil at the time seed was sown and both 

 inoculum and seed covered to the depth of about % inch with additional 

 soil or sand, also steamed. Three-inch pots were most commonly used, 

 and all pots received equal quantities of seed, determined in some experi- 

 ments by count, in some by weight, and in some by volume, or quantities 

 proportional to their areas in the few cases in which pots of different 

 sizes were used in the same experiment. The number of seeds used 

 was in most cases somewhat greater, and in a few cases much greater, 

 than would have been used on an equal area of seed bed in ordinary 

 nursery operations. Partial seed disinfection by sulphuric acid was 

 practiced in a few cases, but not for the most part, as there are no indi- 

 cations that the seed carry parasites to any considerable extent. The 

 inoculum used was the surface layer of an apparently pure culture of 

 the test fungus on prune or corn-meal agar, occasionally on steamed 

 rice or corn-meal mush, and therefore included both nutrient substratum, 

 mycelium, and in most cases spores, except in the case of species of 

 Corticium and Botrvtis, which were not observed to form spores on any 



