Vlll ^ PREFACE TO THE 



Student of botany is taught, that humus becomes the 

 food of plants only by combining with the oxygen of ' 

 the atmosphere and forming carbonic acid gas, and 

 hence the great importance of preserving the roots of 

 plants in communication with the atmosphere, which 

 is the great source of oxygen." . 



In noticing the effect of alkalies, Professor Lindley 

 remarks, that it will lead to the explanation of many 

 things that were inexplicable before. " When it is 

 said, that a plant becomes tired of a soil, and we find 

 that manuring fails to invigorate it, the destruction of 

 alkalies in the soil, and the want of a sufficient supply 

 of those bases in the manure, seem to ofier a solution 

 of the enigma. And in like manner the gradual de- 

 cay of trees in public squares and promenades, where 

 the soil is incessantly robbed of alkaline matter for 

 the sake of neatness, may probably be ascribed to the 

 same cause. So also the injurious action of weeds is 

 explained, by their robbing the soil of that particular 

 kind of food which is necessary to the crops among 

 which they grow. Each will partake of the compo- 

 nent parts of the soil, and in proportion to the vigor 

 of their growth, that of the crop must decrease ,* for 

 what one receives the others are deprived of." 



"It is impossible for any one acquainted with gar- 

 ^ dening not to perceive the immense importance of 

 these considerations, which show, that by adopting 

 the modern notion, that the action of soil is chiefly 

 mechanical, the science of horticulture has been car- 

 ried backwards, instead of being advanced ; and that 



