288 PRINCIPLES OF GARDENING. [CH. VIJI. 



of branches over the mass of roots, by old age, 

 or by the disorganization of the roots in an ungenial 

 soil ; they render the tree incapable of extracting 

 sufficient nouiishment from the soil, consequently 

 incapable of developing a sufficient foliage^, and 

 therefore unable to digest and elaborate even the 

 scanty sap that is supplied to them. 



The reason of the sap becoming unnaturally saline 

 appears to be, that in proportion as the vigour of 

 any vegetable declines, it loses the power of select- 

 ing by its roots the nourishment congenial to its na- 

 ture. M. Saussure found in his experiments, that 

 the roots of plants, growing in saline solutions, 

 absorbed the most of those salts that were injurious 

 to them, evidently because the declining plant lost 

 the sensitiveness and energy necessary to select and 

 to reject. 



M. Saussure also found, that, if the extremities of 

 the roots were removed, the plants absorbed all 

 solutions indiscriminately^. 



An imgenial soil would have a debilitating influ- 

 ence upon the roots in a proportionate, though less 

 violent, degree than the sulphate of copper, and as 

 these consequently would absorb soluble bodies more 

 freely, and Avithout that discrimination so absolutely 

 necessary for a healthy vegetation, so the other 



* No sjinptoms of a cankered tree is more inYariable than a 

 deficiency of leaves. 



•» Saussiire's Recherches Chimiques sur la Vegetation^ 260. 



