8 



PRINCIPLES AND PRACTICE OF PRUNING 



after wilting for several days, but reviving during the night, finally 

 dried out and died, evidently because sufficient moisture was not 

 furnished by the slow-growing Marianna roots to meet the demand 

 from the peach leaves during a period of excessive transpiration."* 



9. Water is absorbed by the root S3'stem of the great 

 majority of higher plants, especially those used in agri- 

 culture and horticulture. This system is of various forms, 

 textures and distributions in the soil, but these differences 

 are not necessarily linked with noticeable differences in 

 the quantities of available water. Root systems may be 

 divided into two general classes, namely: (1) The tap- 

 root style, which penetrates the soil more or less vertically 

 downward (parsnip, hickory), with branch roots de- 

 veloped at irregular intervals ; (2) the fibrous-root style, 

 which reveals little, if any, main root axis, but has many 

 more or less uniformly sized small roots starting from 

 near the l)ase of the stem (wheat, currant). 



10. Root hairs and their function. — Roots and rootlets, 

 no matter how minutely they divide, are both the hold- 

 fast organs whereby plants maintain their positions in the 

 soil, and the pipe lines whereb}- the upper parts of plants 

 are supplied with water taken from the soil. Neverthe- 

 less thev are of secondary importance to the root hairs 

 with respect to the water supply. The root hairs are 

 single cells which push out from the epidermis of rootlets, 

 not at the immediate and elongating tip, but just in the 

 rear of this part, an area that has ceased to extend, but 

 has not developed thick or hard-walled epidermal cells. 

 Their function is to secure water and crude plant food — 

 mainl}^ of a mineral nature — from the soil. Always they 

 occupy positions within a few inches of the extreme tips 

 of the rootlets. As the tips push forward new root hairs 

 are formed in front of the older ones and the oldest dis- 

 appear, to be replaced by thicker-walled tissues incapable 

 of absorbing either water or mineral matter from the soil. 

 Root hairs can be easily studied by sprouting seeds and 



* Kains, Plant Propagation, Greenhouse and Nursery Practice, Pcge 189. 



