400 BOTANICAL GAZETTE [may 



sides) on 3-year or even 4-year-old wood. Some vestige of it 

 often remains a year or two longer, but usually after this time it 

 begins to slough off. 



It was not until some young trees of Amygdahts Davidiana, 

 which were making an extremely rapid spring growth, were 

 examined that the separation which Cook described was found. 

 Ordinarily it requires some effort to remove the dry scalelike 

 remnant left after the fall of the leaf, and usually there is more 

 or less tearing of the bark; but in the case of Amygdalus Davidiana 

 this structure separated easily and clearly when started with a 

 knife point. In many cases after the rapid spring growth it 

 cracked and separated without any outside stimulus, and later a 

 large proportion fell as a result of further enlargement at the 

 node. The condition is represented in fig. 5, which shows the 

 separating scale, and fig. 31, which shows its structure in greater 

 detail. 



Examination of rapidly growing shoots of other Prunus species 

 showed that a similar separation may take place, especially in 

 some of the P. BesseyiXP. triflora hybrids, although 



iharply 



xplanation 



of the fact that the separation of the scar scale occurs in some 

 species of Prunus and not in others, can be made on the basis of 

 the character of the swelling of the node below the leaf insertion. 

 When it is straight in outline, it makes an acute angle with the 



terminates 



m 



tissue underneath forces off the dead scale at the apex. If, how- 

 ever, the node is swollen, with a rounded profile, and the leaf scar 

 is well buttressed below, as in the extreme type shown in fig. 4> 

 the scale does not separate, and cannot be removed without tear- 

 ing the bark. In either case, whether separation is immediate 

 or delayed, it is only the shedding of dead tissue, just as bark is 

 shed, and is done without the aid of a definite abscission zone 

 (Loyd 9), and consequently is not true abscission. 



A search for corroborative evidence as to the nature of this 

 structure showed that in a number of genera it is not uncommon 

 for clean cut separation of a scar scale to occur when rapid growth 



