REPRODUCTION OF WESTERN YELLOW PIXE. 35 



tinctly dominant, pine reproduction is usually deficient. The soil 

 in such situations is usually a deep, stone-free clay. Muhleribergia 

 montana predominates on the stony or gravelly soils, excepting in 

 the most rocky situations, where Andropogon scoparius is usually 

 more abundant. In either case reproduction is usually good. Vicia 

 americana and Lotios icrightii are common associates of Muhlen- 

 bergia montarut and indicate a good site for pine reproduction. 

 Lupinus hillii and several other broad-leaved plants occur mainly 

 where the original grass cover has been disturbed. This subject is 

 discussed in greater detail under "Herbaceous vegetation." 



Mechanical analyses. — Mechanical analyses have, as a rule, failed 

 to bring out consistent relationships between success of reproduction 

 and the physical composition of soils. In the light of recent findings, 

 this is attributed to the fact that in the analyses which have been 

 made, following the conventional method, all material above 2 mill- 

 imeters in diameter was disregarded. It is now known that in the 

 clay soils of this region the particles above 2 millimeters in diame- 

 ter may be of far greater importance than the fine gravel or sand, 

 which are often present only in negligible quantities. 



Chemical analyses. — Chemical analyses have likewise failed to 

 throw much light on the problem. This does not mean that chemical 

 composition is unimportant, but rather that within the areas now 

 occupied by western yellow pine the chemical variations apparently 

 are not sufficient to affect reproduction appreciably. The only sug- 

 gestion of unfavorable conditions due to chemical composition of 

 the soil is in the lower portion of the yellow pine type, where Veatch 

 (25) has found indications that the occurrence of yellow pine may 

 be limited by the presence of excessive quantities of calcium car- 

 bonate. If such a condition does exist, it is probably a consequence 

 of deficient precipitation, so that the calcium carbonate fails to 

 leach out as it does in the higher altitudes, where precipitation is 

 more abundant. 



HOW MECHANICAL COMPOSITION OF SOIL AFFECTS GROWTH OF SEEDLINGS. 



Although much remains to be done on the soil problem, it is be- 

 lieved that substantial progress has been made in establishing a rela- 

 tionship between reproduction and gross physical characteristics of 

 the soil, as determined by the presence of varying amounts of sand, 

 gravel, and stones. This information is especially valuable to the 

 forester, because it can be readily understood and applied without 

 special training in soil physics. Thus far, however, we have merely 

 established the fact that reproduction is best on the coarse-grained 

 or stony soils. Although the fact itself is important, it can not 

 be employed to the best advantage without an understanding of the 



