34 



Plants and their Wavs in South Africa 



This takes place in various ways. A special separation- or 

 absciss-layer is formed by cells at the base of the petiole with 

 or without their renewed activity. The middle wall plate of 

 the absciss layer becomes mucilaginous, the cells round off and 

 easily separate. The veins which are last to be severed become 

 closed with gum and by pressure of surrounding cells. In the 

 meantime a layer of corky cells has formed just below the 



I-'IG. 38. — Apple Stem. Section through (L) a lentice! (winter), X, .\ylem or 

 wood ; Ca, cambiuni ; P, phloem ; Ck, cork ; Cor, cortex ; L, lenticel. (From 

 Farmer's " Practical Introduction to the Stucly of Botany".) Photo Micro. 



absciss layer; these again may be the modified cells already 

 present, or division may take place, the active cells being con- 

 tinuous with the cork camhium of the stem. The cork 

 cambium may remain active for a time alter the leal has fallen, 

 the scar thus becoming well protected. 



Pines, Araucaria (Monkey Puzzle), and its relatives cut 

 off dwarf branches which carry a number of leaves with them. 



The absciss layer is formed by living cells. If a branch is 

 broken so that it hangs by the bark only, the water supply is 



