408 CONSERVATIVE ORGANS. [LECT. VIII. 



part in the majority of ligneous dicotyledons. 

 While it remains entire, the young tree may be 

 regarded as composed of two similar cones united 

 at their bases ; the one rising vertically, or nearly 

 so, above the surface of the soil, and the other, 

 which forms the root, taking the opposite direc- 

 tion and penetrating the earth by constant ad- 

 ditions made to its apex. The place of their 

 union is distinguished externally by an im- 

 pression as if a cord had been tied very tightly 

 round the stem ; and is that part which the French 

 term collet, in the first evolution of the plant in 

 the germinating seed. If the apex be destroyed, 

 it ceases to elongate in the direction of its axis, 

 and shoots out lateral branches ; but these are 

 given off at various other parts also during its ex- 

 tension, and form divisions resembling those of 

 the trunk and the branches above ground. 



b. The RADICLES. The medulla disappears in 

 the radicles, whether they be given off from the 

 caudex or a branch ; but something like the me- 

 dullary sheath is still present. The radicle, there- 

 fore, consists of a spongy centre, resembling the 

 medullary sheath devoid of spiral vessels, sur- 

 rounded by a circle of ligneous vessels, which are 

 either cribriform as in the Horse Chesnut, or annu- 

 lar as in the Vine (the character of the vessels in 

 the radicle being always the same as that of those 

 in the stem and branches) ; and a bark, which is 



