Examining growth rates for experiment A, table 4 shows that both the distilled 

 water control and the rain were significantly greater than the green needle 5 and 10 

 percent, and the 5x Hoagland's solution. In addition, the rain was greater than the 

 roots 5 and 10 percent. In experiment B, both the distilled water and the rain were 

 significantly greater than roots 5 and 10 percent, duff 10 percent, and green needle 

 5 and 10 percent. 



The pH of the test solutions had very little influence on the radicle growth of 

 pine seedlings. However, the radicle growth rates of seedlings in solutions with low 

 osmotic potential were significantly lower than for seedlings in solutions of high 

 osmotic potential, suggesting that osmotic potential was important. The growth of 

 ponderosa pine radicles is very sensitive to osmotic potential and generally decreases 

 quite rapidly as the osmotic potential decreases (Larson and Schubert 1969, Djavanshir 

 and Reid 1975, Rietveld 1975) . Therefore, some of the reduction in radicle growth 

 associated with 5x Hoagland's (-3.2 atms) and green needle 10 percent (-2.3 atms) can 

 be attributed to their low osmotic potentials. 



The green needle extacts both 5 and 10 percent might have contained a phytotoxin, 

 because they significantly reduced germination and radicle growth rates. However, the 

 significance of the green needle results was reduced by the occurrence of fungal and 

 bacterial growth in both experiments A and B. It was the only solution tested that 

 became significantly contaminated. Daily visual observations suggested that the bac- 

 teria and fungi did not become important until the later half of each experiment and 

 probably had less influence on germination than on radicle growth. From these visual 

 observations, it was clear that the green needle extracts did reduce radicle growth of 

 the pine seedlings, but the final results were a combination of extract and fungal 

 effects. In addition, the osmotic potential of the green needle extracts was low 

 enough to be a contributing factor to the reduced radicle growth, but not low enough 

 to have reduced germination. It can be concluded that the germination results for the 

 green needle extracts are reliable, but the results for the radicle growth are question- 

 able. If the green needles of ponderosa pine do contain a phytotoxin, then the toxin 

 could be washed from the needles during a rain storm. Therefore, the activity of 

 throughfall could help in evaluating the presence of a green needle toxin. There was 

 no significant difference in germination or growth between throughfall and pure rain 

 treatments in either experiment A or B. This, however, does not eliminate the presence 

 of a very weak toxin in the throughfall that accumulates with time on the forest floor. 



There are three other plant extracts, roots, duff, and bark that could also con- 

 tain a phytotoxin. Both the 5 and 10 percent solutions of roots significantly reduced 

 radicle growth compared to the rain in experiments A and B and to the distilled water 

 control in experiment B. The root extracts had less effect on germination, with a 

 significantly lower germination than rain in experiment B. This suggests the presence 

 of a growth inhibitor within the roots of ponderosa pine. The severity of inhibition 

 is certainly not great as seen in table 3. In the field, pine seedlings germinate on 

 or near the soil surface well above the roots of pine trees; it is very unlikely that 

 this weak toxin would influence seed germination and initial root growth; however, it 

 might influence the later root development. 



The germination of seeds in duff 5 and 10 percent solution was significantly lower 

 than rain only in experiment B. Duff 10 percent also reduced radicle growth rates 

 significantly below the control and rain in experiment B; there was no significant 

 difference in experiment A. If there is a toxin present in duff extracts, it is very 

 weak because only the 10 percent solution demonstrated much activity. 



The bark 10 percent and its natural counterpart, stemflow, reduced germination 

 compared to rain in experiment B. Neither solution interfered with the radicle growth. 



9 



