ROOT. 17 



Stance thus cast off by themselves and by the 

 otlicrs around. And why young apple trees 

 planted on the site of an old apple orchard 

 cannot thrive, the earth is full of the poisonous 

 matter thrown off by the roots of the old trees ; 

 but probably young cherry or peach trees 

 would succeed. Likewise it accounts for the 

 natural rotation of trees which has been dis- 

 covered to exist in the ancient forests of this 

 part of the globe ; for the necessity of repot- 

 ting plants grown in green-houses every one 

 or two years, and for m.any other circumstances 

 in horticulture for which hitherto sufficient 

 reasons had not been given. 



Much of the healthy action of the root de- 

 pends on the warmth and moisture of the soil. 

 A late German writer, Mr. Writgen, has made it 

 appear probable that much more depends on 

 this than on the geological nature or chemical 

 state of the soil, and when it is considered that 

 the salts usually found in the earth are more 

 readily soluble in a warm moisture than in a 

 cold one, and also that heat is favorable to 

 decomposition and the production of gases — it 

 seems likely there is truth in this position. 



During the summer in the temperate parts of 

 Europe, the earth at one and two feet depth is 

 2* 



