178 



HUTCHINSON'S POPULAR BOTANY 



direction. The experiment did not end here. For upwards of twenty years 

 Colonel Greenwood preserved one of the plants in its inverted position,* by 

 placing it on a flat stone and exchanging the flower-pot, when the branch- 

 root grew too long for it, for a chimney-pot full of earth ; and so adding 

 another and another, as occasion required, till the column was seven feet 



high. Then he turned the root over a wall 

 into a similar column of earth on the other 

 side, thus permitting it to take, for the 

 first time, a downward direction. When 

 at last this much-abused organ reached 

 the ground, the colonel removed both of 

 the artificial columns ; and the plant, with 

 a naked, arching root, fourteen feet in 

 length, was left to its own resources 

 (Athenceum, 1864). 



Seeing that roots are such wonderful 

 we had almost said versatile organs, it 

 may be interesting to look a little at their 

 structures. The root-section shown (fig. 

 224) is that of a young Maple (Acer 

 campestre). Notice particularly the layers 

 of rather long cells (a) at the extremity of 

 the root. These constitute the root-cap.^ 

 and form a sort of protecting shield to 

 the dense cluster of smaller cells hidden 

 immediately within the end of the sheath, 

 which form the growing-point of the root. 

 All the wear and tear to which these 

 delicate-growing cells would be subject is 

 borne by the sturdier root-cap ; while the 

 growing-point makes some compensation 

 for the services thus rendered by fabri- 

 cating new cells for the sheath on its inner 

 side, as its outlying cells become worn and 

 withered in the rough pioneer work which 

 they perform. In the centre of the root 

 is a bundle containing woody vessels 

 the vascular cylinder or stele which consti- 

 tutes, in conjunction with the rest of the 

 vascular system, the mechanism by means of which the crude sap is carried 

 upwards to the leaves, there to be elaborated into nutrient material. In 

 nearly every species of plant there is but one of these steles in -each 

 root, but in a few chiefly palms the roots are polystelic. The tissue of 

 * Inverted as regards the root. t The pileorhiza of some botanists. 



FIG. 222. GERMINATION OF THE 

 SEED OF A PINE (Pinus). 



