DEVELOPMENT OF KOOT-SYSTEMS. 235 



been uniformly mixed with a fertilizing substance, and in this 

 soil the roots had developed in a normal manner. In the sec- 

 ond cylinder a laj'er of the fertilizing material had been placed 

 three to four centimeters below the surface, and in the soil at 

 this plane the roots had branched very abundantly. In the 

 third cylinder a similar layer of the fertilizing matter had been 

 placed half-way down the cylinder, and here the root-branches 

 were far more numerous than elsewhere. In other cases the 

 fertilizing substance had been placed at the bottom, around the 

 sides, or in the middle of the cylinder, and in these places respec- 

 tively the root-branches were most abundant. Substantially the 

 same thing is observed in earth where the roots of plants meet 

 with buried bones : the finer root-branches are developed around 

 and afterwards in the substance of the decomposing animal 

 matter, often forming dense mats. 1 



629. In some cases roots extend to very great distances ; 

 thus those of an elm have been known to till up drains fifty 

 yards distant from the tree. 2 It may be said, in general, that 

 the roots of the common forest and shade trees reach to and be- 

 yond the eaves of the roof made by the leafy branches. "There 

 is a constant relation between the horizontal extension of the 

 branches and the lateral spreading of the roots. It is not by 

 watering a tree close to the trunk that it will be kept in vigor, 

 but by applying the water on the soil at the part correspond- 

 ing to the ends of the branches. The rain which falls on a tree 

 drops from the branches on that part of the soil which is situ- 

 ated immediately above the absorbing fibrils of the roots." 8 



630. The root-system of a plant, ever extending by its in- 

 numerable subdivisions into new soil, and clothed near the 

 extremities of the rootlets with delicate epidermal cells, is a 

 complex apparatus for osmosis placed under the most favorable 

 conditions for absorption. 



631. The course of the water after it has found its way into 

 a plant through the epidermal cells of the newer portions of the 

 roots, and the pressure which at times the watery liquids in roots 

 exert, can be more conveniently examined at a later stage (see 

 Chapter IX., " Transfer of Water through the Plant "). 



1 See also a paper by Detmer : Versuchs-Stationen, 1872, p. 107. 



2 Journal Royal Agricultural Society, vol. i. p. 364, contains some interest- 

 ing cases of great length of roots. 



8 Balfour ; Class Book of Botany, 1854, p. 427, 



