io8 



BOTANY FOR BEGINNERS 



CHAP. 



sequently dry up and aid in the formation of bark. The parts 

 which form bark and periderm are shown below : 



{Phelloderm 

 Phellogen 

 Cork cells 



Bark. 



Cork cells 

 Endodermis 

 Cortex 

 Epidermis 



The primary phellogen after a time ceases its activity, and a 

 deeper phellogen is formed. Still later, even this may discontinue 



FIG. 134. Transverse section through 

 stem of Maple. D, dried up epi- 

 dermis and cortex ; C, 'cork cells ; 

 PH, phloem ; XY, xylem. (X 150.) 



FIG. 135. L, Lenticel from the stem of 

 the Lilac. (X25) PD, phellogen ; 

 PL, phelloderm ; E, epidermis. 



its function, until at last the new phellogens which are produced 

 come to be formed in secondary bast. If the bark which is 

 produced by these deeper phellogens is thrown off in scales 

 it is called Scaly bark ; this is found on the Pine and Plane 

 tree. On the other hand, if the secondary bark forms complete 

 rings which are concentric ringed bark is formed, as in 

 the Honeysuckle, Clematis, and Grape-vine. 



Lenticels. In the Periderm are produced small _ pores 

 called lenticels. They are developed just beneath those places 

 where the stomata existed in the epidermis. They are openings 

 formed by the phellogen, which produces cells between which 

 intercellular spaces are formed (Fig. 135). 



EXPT. 101. Prepare sections of the flower stem of the White Lily, 

 and if the stem is fresh, mount the thinnest section in water ; if the 

 material has been in spirit, mount in glycerine. Observe 



(i) The epidermis, a single layer of cells. 



