CLIMATE AND PLANT GROWTH. 7 



THE SOIL. 



The soil surface exposed by the perforations in the lids was pro- 

 tected from evaporation by a thin layer of wax consisting of a mix- 

 ture of 3 parts of tallow and 7 parts of beeswax, applied in a melted 

 condition. 



The soil of the region is, in the main, of limestone origin, conse- 

 quently soil of that type was selected. Except for the purpose of 

 determining the relation of plant growth to soil fertility the soil 

 used was taken from the upper 6 inches in a single situation in the 

 aspen-fir type, and was uniform throughout all the potometers. In 

 order to eliminate pebbles, roots, and other decomposed organic 

 matter the soil was sifted through a J-inch wire mesh. Because of 

 the presence of a large amount of clay the native soil is not so porous 

 as was desired, and for this reason sand was mixed with it in the 

 proportion of 5 parts of soil to 1 part of sand. The soil used was 

 rich in humus, 5 samples averaging 12 per cent by weight after mix- 

 ing with the sand. The addition of the sand reduced the wilting 

 coefficient somewhat, the average being approximately 15 per cent. 



After the soil was thoroughly mixed in the air-dry state, water 

 was sprinkled over it until it had a " fresh " consistency ; that is, 

 the particles adhered in a lump when squeezed in the hand. Soil 

 samples taken from each batch of soil after mixing and watering 

 were found to average 31 per cent humidity, the variation being from 

 28 to 34 per cent. The moist soil was moderately tamped in the 

 potometers, so as to prevent breaking of the roots by cracking and 

 settling of the soil when .drying. The weight of the moist soil in the 

 potometers averaged 135 pounds. 



EFFECT OF SOIL FERTILITY ON WATER REQUIREMENTS AND GROWTH. 



While it has long been known that the development of the plant 

 and the amount of water required for the production of a unit of dry 

 matter may vary widely according to the texture and fertility of the 

 soil, 1 it was deemed advisable to determine the difference in water 

 requirements and growth of plants developed in soils of the same 

 origin and texture, but differing appreciably in organic matter. The 

 two soils investigated were of limestone- origin and formed within 50 

 yards of each other in the spruce-fir type at about 10,000 feet eleva- 

 tion. They may be briefly described as follows: 



(1) Infertile clay loam. The soil was well disintegrated, but owing 

 to the destruction of most of the ground cover erosion and washing 

 had diminished the humus content and to some extent the soluble 

 salts. 



1 Sachs. J., Bericht ubor die physiologische Th-itigskcit an dor Versuchsstation in 

 Tharandt. Landwirthschaftlichon Versuchsstationen. Vol. 1 : 235. 1859. 



