HORTICULTURAL RESEARCH 



283 



Root-growth 



A root grows by elongation from the tips and unless such 

 elongation be in progress, either in the root itself or in laterals 

 arising from it, the root ceases to fulfil its functions and the 

 tree dies. The extension of a root depends solely on the 

 presence of certain cells which are capable of multiplying and 

 then elongating; these meristematic cells, as they are called, 

 form a small group situated at the end of the root-tip and are 

 protected from injury by certain outlying cells which constitute 

 the root-cap. The latter are continually rubbed off as the 

 root pushes its way through the soil and are continually 

 reproduced from the region containing the meristematic cells. 



Fig. 3. 

 c, Central cylinder ; w, Wood vessels R, Cortex ; e, Epidermis ; H, Root-hairs ; 



M, Root-tip ; k, Root-cap. 



The whole root-tip is very minute, indeed microscopic, so that 

 it is impossible to lift a tree for the purpose of transplanting 

 it without breaking off most of the root-tips ; even if they are 

 not broken off, the unavoidable exposure to the air causes 

 them to dry up and to become useless : the continued existence 

 of a tree after transplanting must, therefore, depend on the 

 formation of new root-tips. There are no cells at the cut or 

 broken end of the root able to do this but there are cells 

 situated at intervals throughout the length of the roots which 

 are capable of becoming meristematic and of giving rise to new 

 root-tips, eventually forming new roots branching from the 



