Germination of Forest Trees 83 



Burns reached the conclusion that shade reduces the temperature 

 of the soil and delays germination. Evidently there is a delicate 

 balance between soil moisture and soil temperature, so that a 

 slight deficiency in either might delay the germination process. 

 In Burns's case the temperature of the soil was so low, that in 

 spite of the fact that there was sufficient soil moisture, germina- 

 tion was delayed. In the present investigations soil temperature 

 was kept at an optimum and measured differences in soil moisture 

 were sufficient to result in an acceleration of germination in the 

 shade cultures. One unfortunate fact about Burns's work was 

 that he failed to take into account soil moisture. In his experi- 

 ments it must be assumed that there was sufficient soil moisture 

 for germination. But there is nothing in his report which does 

 not indicate that there was too much soil moisture. The recip- 

 rocal relation between soil temperature and soil moisture is well 

 known. Furthermore there is an intimate relation between soil 

 moisture and soil aeration and germination. Such factors as 

 these were evidently not taken into account to explain the delay 

 in germination in the experiments cited. 



3. Shade increases the length of the germination period. This 

 bears out to a certain extent Pittauer's experiments which showed 

 that germination proceeds more rapidly in the light than in the 

 shade. 



4. The germination curve of seeds sown in the shade rises more 

 rapidly than the curve of seeds sown in the light. This con- 

 clusion does not agree with the results obtained by Pittauer. 



5. The final germination per cent, is usually higher in the case 

 of seeds sown in the shade than those sown in the light. This 

 conclusion, based upon abundant evidence, is not in accord with 

 some work done by Atterberg which showed a greater germina- 

 tion per cent, in the presence of light than in the absence of it. 



— ■ 6. Light plays absolutely no part in the germination of tree 

 seeds; in fact shade has been found to be exceedingly beneficial 

 to germination, other factors being equal. In the work carried 

 on by Burns already referred to, there are at least two state- 

 ments that a certain amount of light is necessary for satisfactory 

 germination. Whether he means to imply by the term " light " 



