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fruit trees are careful not to attempt to grow two successive crops on 

 the same land. Even after employing all kinds and qualities of ma- 

 nures that their skill and experience may suggest, the quality of their 

 young stock will depreciate if grown on the same soil unless long peri- 

 ods elapse between the rotations. These and facts of a similar kind 

 might be assumed as an indication that there may be some as yet un- 

 recognized cause that exerts an influence in plant nutrition. 



Many years ago the hypothesis was advanced that plants secrete or 

 form certain matters during their growth which they exude by their 

 roots, and the accumulation of these ingredients in the soil exercises an 

 injurious influence upon future crops of the same plants, but does not 

 prevent the growth of plants of a different kind. It was even surmised 

 that the exudations of one species furnished nutritious matters for a 

 different species, and for this reason a rotation of crops becomes advan- 

 tageous and furnishes an explanation for the benefits consequent upon 

 the practice. 



The experiments and explanations brought forward in behalf of this 

 hypothesis have not been considered sufficiently conclusive to establish 

 a theory upon which to base any definite action, and has not of late 

 years been entertained as a factor worthy of consideration in the study 

 of plant life or as pertaining to plant culture. And yet every practical 

 cultivator must have observed phenomena in the course of his practice 

 which appears to be more readily explained upon the supposition of the 

 formation of some injurious matters than from the exclusive action of 

 exhaustion ; and this may occur without conceding that there is neces- 

 sarily any function of an excretory character in the roots of plants. 



If we attempt to remove a silver maple tree of 3 or 4 years' growth 

 from the seed we will find that the soil closely surrounding the stem 

 and circling for several feet beyond it is filled with small fibrous roots, 

 mostly dead ; active spougioles will be found mainly at the extremities 

 of the larger or main roots. But if we take a tree of the same species 

 which has attained the age of 10 years and dig similarly around its 

 stem, we will not find so many roots as in the case of the younger tree, 

 but instead we will find a few large roots which are destitute of fibers 

 except at their extremities. It seems evident that there is an annual 

 decay of these fibrous roots, and it is a question whether the decom- 

 position of this mass of fiber may not be obnoxious to the plants which 

 produced it, and at the same time not be injurious to plants of a differ- 

 ent species. 



Instructions relative to the removal and replanting of trees are usually 

 very explicit in regard to the special necessity of protecting the small 

 fibrous roots because of their great importance to the future growth of 

 the plant. In reality these roots are of no value after they are sep- 

 arated from the soil, as they immediately decay on removal. The 

 larger roots, if healthy and their outer bark uninjured, are only to be 

 depended upon for the emission of an abundance of fresh and vigorous 

 spougioles. 



