94 



This dropping is due, not to l.reaking, ),nt to growing;- off by the forma- 

 tion of a cleavage plane between both the twig, petiole and the parent 

 stem. Thus the reason for the scars left by the shedding 



In the shedding of stems, the cleavage plane is graduallv developed 

 across the flbro-vascular system separating the stem from the parent 

 stem with the exception of the bark and a few layers of wood cells which 

 are easily broken. The scar is virtually formed before the falling of the 

 stem. Marked illustrations of this habit from the deciduous trees are 



fouud in the family Salicacen« L. Tlu- brauHus and twigs begin to fall 

 before the shedding of the leaves and c-ontinu. tln-oughout the period of 

 leat fall. The twigs shed are green, m.any bearing large winter bnds 

 upon their tips. Of the conifers, the Ts.,,, ,UnunIn,sis Carr., illustrates 

 llHs habit very m.arkedly. However, their twigs, wlien shed, are dead.* 



m the shedding of leav(-s. we find the form.ation of the cleava-e 

 l.lane the same as in the stem. The most common method is that of 

 a separation between the petiole and stem, as shown by the scars on the 

 stems. 



■ The Self-pruning of Woody Plants.-John H. Scliaffner, Ohio Nat. I., 1902, pp. 17M47 



