116 



SIZES OF LEAF-SCARS 



[CH. 



stage, profoundly affect the whole branch-system later on ; 

 and we shall see that there are numbers of other cases 

 of arrest of onward growth of the twigs to be considered 

 subsequently. 



The leaf-scars are the surfaces of insertion whence the 

 leaves have fallen, covered with a thin protective layer of 

 cork, formed beneath the separation-layer (absciss-layer) 

 which brought about the cutting off of the leaf from the 

 stem as described on p. 105, and their position of course 

 marks that of the previous leaves i.e. they are closely 

 crowded, opposite or alternate, spirally arranged or distich- 

 ous, accordingly. 



Leaf-scars differ much in size, in shape and in promi- 

 nence; the latter according as the absciss-layer was formed 

 close to, or further up the leaf-stalk from, the plane of 

 insertion of the leaf. 



The following have large leaf-scars : 



Horse-chestnut Walnut Ailanthus 



Ash Elder Fig. 



That is to say in cases where the leaves are large and 

 have a large pulvinus at the base of the petiole. 

 In the following the leaf-scars are very small : 



