36 THE OAK. 



The root of the oak, speaking generally, is a typical 

 root in the following respects : It consists, as we have 

 seen, of a primary or tap root which develops secondary 

 or lateral roots in acropetal succession, and these in 

 their turn produce rootlets of a higher order. These 

 secondary, tertiary, etc., rootlets arise endogenously, 

 taking origin from the pericycle at the periphery of the 

 strand of vascular bundles which traverse the central 

 axis, and then bursting through the cortex to the ex- 

 terior. The primary root, as well as the rootlets of all 

 orders, are provided with a root-cap at the tips, and 

 they all agree in being devoid of chlorophyll or stomata. 

 From the outer layer of cells the piliferous layer, cor- 

 responding to an epidermis root-hairs are developed at 

 some little distance behind the root-cap, and these su- 

 perficial cellular outgrowths also rise in acropetal suc- 

 cession, the older ones behind dying off as the younger 

 ones arise farther forward. If we bear in mind all 

 that has been shortly stated above, it will be very easy 

 to figure the behavior of the root-system as it pene- 

 trates the ground, and the following short description 

 of the biology of the root may render the matter clear. 

 When the radicle commences to bore down into the soil 

 it puts forth a large number of root-hairs from the 

 parts a few millimetres behind the tip, and these attach 

 themselves to the particles of soil and supply points of 

 resistance; the tip of the radicle is protected by the 

 slippery root-cap, and it must be borne in mind that 

 the embryonic tissue of the growing-point consists of 



