be Se i Ee | al RES REPT: f 1a o vet 
962 »=REPORT OF THE COMMISSIONBR OF AGRICULTURE. 
cupied with grapes, the young plants will make an average growth 
of about four feet in length the first year; the average growth of the — 
second year will reach about two feet ; the growth of the third year will 
be exeeedingly weak, the best plants reaching to about eighteen mches 
in length, many weak kinds not reaching the length of one foot. 
This result of diminishing yearly groavils bas not been sensibly af- 
fected by the application of different manures, and the question natu- 
rally arises that if a deterioration of growth becomes so marked in so 
short a time, and with such attention to the soil, what may be expected 
when acres are closely planted with grapes, as in the case of vineyards, — 
where the entire soil speedily becomes filled with roots? It need not 
be a matter for surprise if vineyards become unproductive after produc- 
ing several satisfactory crops. 
it is well known that nurserymen who pride themselves in maintain- 
ing a high standard of quality in their stock of pear or other kinds of 
fruit trees are careful not to attempt to grow two successive crops on 
the same land. Even after employing all kinds and quantities of man- 
ures that their skill and experience may suggest, the quality of their 
young stock will depreciate if grown on the same soil unless long periods © 
elapse between the rotations, These and facts of a similar kind might 
be assumed as an indication that there may be some, as yet unrecog- 
nized, 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 aceumulation of these ingredients in the soil exercises an 
injurious influenee 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 dif- 
ferent 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 conelusive 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 
eultivator 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 three or four 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 smail fibrous 
roots, mostly dead; aetive spongioles will be found mainly at the ex- 
tremities of the larger or main roots. But if we take a tree of the same 
species which has attained the age of ten years and dig similarly around 
its stem, we will not find so many fibrous roots as in the case of the 
younger tree, but instead we will find a few large roots which are desti- 
tute of fibers except at their extremities. It seems evident that thereis 
an annual decay of these fibrous roots, and it is a question whether the 
decomposition 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 
different species. 
Instructions relative to the removal and replanting of trees are usu- 
ally very explicit in regard to the special necessity of protecting the 
