THE STRUCTURE OF THE ROOT 7 



lower cells, from which they have: been withdrawn ;in their 

 turn, absorb from still lower cells, and these ultimately from 

 the root-hairs. Thus a continuous current of nutritive salts 

 is established through the cell-walls, beginning in the root- 

 hairs and extending to the vessels which occupy the central 

 cylinder of the root, and through which they are forced with 

 great rapidity to the upper regions of the plant. 



But even solid mineral particles can be made use of by the 

 root-hairs. For these cells give off carbonic acid and also non- 

 volatile acids, which act upon the particles, dissolve them, 

 and absorb the solution. This process can be very readily 

 and effectively demonstrated by growing seedlings under a 

 very thin covering of soil on a polished piece of marble. After 

 a short time those rootlets which have come in contact with 

 the marble plate will be found to have etched their course over 

 its surface. This they will have done by dissolving away the 

 marble from those places where they have been in contact 

 with it. 



(&.) The Boot- Tip. 



It is of great importance to the gardener who wishes to 

 regulate the growth of roots to suit his own purposes, to 

 understand the structure of that part of the root in which 

 growth takes place. The latter depends, first, upon the forma- 

 tion of new root-cells ; secondly, upon the elongation of these 

 cells. 



We should, however, be making a mistake were we to 

 assume that the formation of the tissues which cause the 

 elongation of the root takes place in the same way as it does 

 in the case of the shoot. In the latter the tip, at first pro- 

 tected by bud-scales, is afterwards generally uncovered, and is 

 built up of very delicate, closely packed cells, rich in proto- 

 plasm and divided by new transverse walls. The extreme tip 

 of this actively growing region (meristem) is continuously 

 giving rise to new Cells during the whole vegetative period, and 

 the increase in length of the axis is due to the growth of each 

 of the new cells to_ its mature size. 



In the case of the root, too,, we find, it is true, the same 

 method of arrangement, and increase of the meristematic 



