Animal Morphology. 139 



not deep. So of different kinds of apple, pear, and plum 

 trees of twenty to thirty years' growth, in a large orchard, 

 some. will be more dentated, or serrated, than others, and 

 the bark will agree much with the condition of the leaf. 

 There is one remarkable exception, and that is in the com- 

 pound pinnated leaf of the common acacia (Robins pseud- 

 acacia), where the leaf is ver} r smooth round its borders, and 

 the bark is very deeply grooved and rough. Upon carefully 

 examining this leaf, it appears almost as if the mid-rib was 

 a continuance from the petiole, and the leaflets were really 

 transverse or side-ribs, called lateral nerves, with the paren- 

 chyma interrupted or arrested in its development, and 

 therefore formed of a succession of apparently real leaflets. 

 If such should really be the case, then the deep rough 

 fissuring of the bark only confirms the general statement 

 here made. 



Again, the roughness or smoothness of the bark is not 

 the only point connected with the bark which is connected 

 with the form of the leaf; for, in some trees, the bark scales 

 off in patches or flakes, and does not appear to groove in the 

 line of the long axis of the trunk, nor at any angle with that 

 far short of what might be termed, in rather freely-used 

 language, at right angles to the long axis. In such trees the 

 leaves appear to be broader at right angles to the mid-rib than in 

 the direction of the mid-rib as, for instance, the bark of the 

 sycamore tree scales off in flakes and does not fissure ; also 

 the very singularly arranged bark, or cellular integument of 

 the birch, which peels off in a circle, and yet is deeply 

 fissured in the bark in old trees ; but the leaf is well serrated 

 on its borders, and is as broad transversely as in the line of 

 the mid-rib. 



Again, the stem as a whole, in the last year's shoots, or 

 growth, is much more frequently found quadrangular in 

 evergreens, or trees which, though not evergreens, yet retain 



