a natural leachate of green needles, did not inhibit seed germination. However, the 

 two artificial green needle solutions were probably more concentrated than the through- 

 fall, hence the increased inhibition. The natural stemflow may have been more concent- 

 rated than either of the prepared bark solutions because it was slightly inhibitory, 

 whereas the prepared solutions were not. 



The radicle growth rates of seedlings exposed to pure rainwater were significantly 

 greater than growth rates in the 5 and 10 percent root solutions, the 5 and 10 percent 

 green needle solutions, the 10 percent duff, and the 10 percent litter solutions. Again 

 both green needle solutions were inhibitory, but throughfall was not. Some of the inhib- 

 itory effects of the green needle solution could be attributed to the osmotic potential 

 of the solution and fungal growth. Recognizing that the solutions used in this exper- 

 iment were highly concentrated, the green needle and root extracts were the two most 

 toxic solutions, and the bark and duff extracts were marginally active. 



In the soil leachate experiments, no significant differences in germination were 

 observed between the distilled water control and any of the leachate treatments. In 

 one replication of this experiment, duff and bark leachates reduced root weights com- 

 pared to controls; however, in the second replication, neither of these solutions were 

 inhibitory. In most cases, both shoot and root weights of seedlings watered with plant 

 leachates were similar to the distilled water controls. 



In the field soil bioassay, pine seed germination was significantly lower in the 

 canopy soils than in the opening soils in duplicate experiments. This may have been 

 caused by differences in soil structure due to larger amounts of organic matter in the 

 canopy soils creating water potential differences. It is also possible that a phyto- 

 toxin was responsible. Although leachate experiments failed to find strong germination 

 inhibitors in pine tissues, it is possible that weak phytotoxins accumulated on canopy 

 soils or were produced by microbial activity. An interaction between a weak phytotoxin 

 and moisture tensions may have also reduced the germination. Shoot, root, and total 

 seedling weights were very similar regardless of treatment. 



Two separate experiments were performed to test the overwintering seedbed effect 

 on germination. In the first experiment, the seeds overwintered in the field on various 

 seedbeds with and without a canopy cover. Seeds away from the canopy influence showed 

 the greatest germination. This may have been caused by increased moisture and the 

 better stratification of seeds under a deep layer of snow in the openings, a weak 

 phytotoxin under the canopy, or both. Seeds stratified on litter, and litter and duff 

 seedbeds had the poorest germination for those seedbeds located away from the canopy 

 influence. 



The second seedbed experiment was set up in the laboratory where the seeds were 

 stratified on a variety of seedbed materials in a coldroom. Germination percentages 

 were very similar regardless of the seedbed. Fungal contamination did not reduce 

 seed viability. 



COIMCLUSIOIMS 



No highly toxic compounds in the live or dead tissues of ponderosa pine, volatile 

 or water soluble, drastically reduced the germination or early growth of ponderosa 

 pine seedlings. 



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