THE PRIMARY ROOT. 



81 



107 



poraneous with this elongation of the radicle, a new and different 

 growth takes place from its lower 

 extremity in a downward direction, 

 which forms the ROOT (Fig. 107, r). 

 The root is therefore a new forma- 

 tion from the root-end of the radicle. 

 It begins by the production of a 

 quantity of new cells (by division) 

 at the extremity of the radicle ; not 

 on its surface, however, but beneath 

 its thin epidermis and the superficial 

 cells. The multiplication of cells at 

 this point proceeds from below on- 

 wards ; those behind quickly expand- 

 ing to their full size, and then re- 

 maining unaltered, while those next 

 the apex continue to multiply by di- 

 vision. In this way the root grows 

 onward by continual additions of 

 new material to its advancing ex- 

 tremity ; lengthening from the lower 

 end entirely or chiefly, so that this 

 part of a growing root always con- 

 sists of the most newly formed and 

 vitally active tissue. 



119. The new cells, however, do not occupy the very point, as 

 is commonly, but incorrectly, stated. This is capped, as it were, 

 by an obtusely conical mass of older cells, consisting of the super- 

 ficial tissue of the end of the radicle, pushed forward by the cell- 

 multiplication that commenced behind it, as already mentioned 

 (Fig. 108). As the original cells of this apex wear away or per- 

 ish, they are replaced by the layer beneath ; and so the advancing 

 point of the root consists, as inspection plainly shows, of older and 



108 



FIG. 107. A germinating embryo of Sugar Maple, still more advanced : a, the radicle elon- 

 gated into the first joint of stem, bearing the unfolded cotyledons or seed-leaves, b, and between 

 them the rudiments of the next pair of leaves; while from its lower extremity the root, r, is 

 formed. 



FIG. 103. The lower end of the same root, magnified: a, the place where growth, through 

 the multiplication of cells by division, is principally taking place : b, the original apex of the 

 radicle, which has been carried onward by the growth that has taken place just behind it. 



