34 Richard H. Bocrker 



Species that seemed to be affected most were those from the 

 Black Hills and New Mexico and those affected least were those 

 from the Pacific coast. Intermediate between these were those 

 species obtained from Montana and Idaho. The coast species 

 affected most was Sequoia washingtoniana. Pseudotsuga taxi- 

 folia was much less affected than Pimts ponderosa taking into ac- 

 count all the varieties of each. 



The conditions and cultures which were favorable to damping- 

 off are of interest in that they emphasize many points already 

 known about this part of the subject. Loam is more dangerous 

 than sand or gravel due to its moisture retentiveness. The shade 

 cultures were more affected than the open light due to a greater 

 soil moisture content in the upper layers of soil. The moist cul- 

 tures were affected more than the dry ones and the shallow soil 

 cultures more than the deep soil ones due to a greater amount 

 of soil water per unit of volume of soil. Humous soils, soils with 

 decaying vegetable matter, and manure soils should be avoided 

 because they contain myriads of fungus spores. The data for 

 Pinus divaricata is given as representative of the three worst 

 affected species. The per cents, given below are those of the 

 number of plants killed (out of the total number that germinated) 

 within five weeks after planting the seed. Two hundred seeds 

 were planted in each culture : 



Pinus divaricata Killed by Damping-off 



Light Cultures Soil Moisture 



Soil Depth 



Soil Texture 



Open 35% Dry soil o% Deep 8%iLoam 35% 



Medium 26% Medium soil. . .24% Medium 35%|Sand 1% 



Dense 90% Wet soil 35% , Shallow 6 i %|Gra vel. . . . . . . 0% 



THE EFFECT OF HABITAT FACTORS UPON GERMINATION 



This problem was undertaken because it was felt to be of funda- 

 mental significance not only to silviculture but to ecology as well. 

 Not only was it desired to throw more light upon some of the 

 phases of this problem that had already been partly worked out 

 and to modify, if necessary, some conclusions that have been 

 drawn, but it was my intention to throw some light upon phases 



