24 CALIFORNIA GARDEN FLOWERS. 



for the composition and activity of soils constitute one of the most 

 complex subjects* with which science has to deal, involving chemistry, 

 physics, botany and bacteriology in some of their most subtle mani- 

 festations. Man has not yet attained mastery of soil science and is 

 now striving for full understanding more strenuously and with better 

 research equipment than ever before. Still many things are sufficiently 

 understood to serve as a guide in soil improvement and to make the 

 teachings of experience more intelligible than hitherto. The reader 

 should study some recently written treatise on soils of which there are 

 many available and all of them edifying along the line of elementary 

 facts and principles most directly affecting practical work. 



Perhaps the most helpful conception the amateur can get of the 

 soil is that it is a sphere of action, of agencies, materials and forces 

 analogous to the activity in the atmosphere. One must not regard the 

 soil as merely "dirt" a mass of dead matter, inert except as a growing 

 plant may lay hold upon it or push it aside. The soil is full of activities 

 which are modifying its components and characters and qualifying it 

 to actively minister to the growth of plants not merely to tolerate it. 

 These activities are very numerous and have directly to do with the 

 ability of the soil to render its proper service to the growth of the 

 plant. A few may be mentioned to indicate their indispensability: 

 1. Mechanical changes in soil particles; granulation induced by earth 



insects, burrowing animals, tillage and chemical changes. 

 2. Chemical changes in soil contents; induced by reactions, fermenta- 

 tions, humus formation, nitrification, etc., by bacteria. 

 3. Air movement; distributing oxygen, nitrogen, carbon dioxide, etc., 



for plant nutrition, directly and indirectly. 



4. Water movement; employing the physical forces of gravity, cap- 

 illarity, absorption, evaporation, etc., generally for the advantage 

 of the plant, but sometimes otherwise. 



Suggestions of the action and inter-action of such agencies and 

 forces as these should lead the amateur to soil study and careful 

 observation of facts encountered in his experience. 



Horticultural Aspects of Soils. Generally speaking it may be said 

 that suitability of soils for horticultural uses is determined by two 

 distinct groups of characters or conditions: first, the physical or 

 mechanical; second, the chemical. When we speak of "heaviness" or 

 "lightness," "coarseness" or "fineness", "tightness" or "looseness", etc., 

 we refer to the physical characters. When we speak of "richness" 

 or "poorness", "fertility" or "sterility", we refer to the chemical 

 character. In a general way it may be said that the physical characters 

 help the- plant to grow, the chemical characters furnish it something 

 to grow with, one may be called "plant-support", the other "plant- 

 food." 



