PRIMORDIAL LEAVES 47 
scale-like phyllodes on the surculi, and the more-definite more- 
membranous primordial leaf as well, may all be held to possess 
no atavistic value, because too unfinished and indefinite. They 
may never reach the full expression of any one of their ances- 
tral stages; like the rudimentary scales produced on the young 
oak seedling before the first leaves. The very crude and scale- 
like but already round-tipped or spatulate first primordials of A. 
ericoides, A, paniculatus, A. puniceus, etc., may be adduced to 
strengthen this explanation. Intercalated minute entire leaves may 
then be explained (though very incompletely) as failures of vigor 
due to temporary unfavorable conditions ; and so with the arrest 
forms. By this explanation A. biformis becomes an example of 
a transmitted arrest-impulse so strong as to hold even in favorable 
conditions and so become measurably permanent. 
