LKCT. X.] ANATOMY OF LEAVKS. 579 



the summit of the petiole, and in this respect 

 have an affinity to digitate leaves, present 

 nearly the same vascular structure of the petiole 

 as the compound leaves. The fasciculi are dis- 

 tinct ; and correspond in number to the princi- 

 pal costse of the leaf; each of which may be thus 

 regarded as a kind of midrib, and the leaf as com- 

 posed of a number of conjoined leaflets: so that 

 these leaves, although they are necessarily classed 

 as simple leaves from their external appearance, 

 yet, bear in anatomical structure the same affinity 

 to digitate compound leaves, which the webbed 

 foot of a bird bears to one which is not webbed. 

 A similar structure, also, is found in the petioles 

 of those leaves which are longitudinally ribbed, or 

 nerved as the common expression is, from the 

 base of the expansion, as for instance those of the 

 genus Melastoma; but, when the ribs do not origin- 

 ate from the base, although they are very conspicu- 

 ous, as, for example, in the leaf of the Cinnamon 

 tree, the structure of the vascular system of the 

 petiole is exactly the same as in simple dicotyledo- 

 nous leaves, which are not longitudinally ribbed. 



If, instead of a transverse section, we place a 

 longitudinal section of any of these leaves under 

 the microscope, we perceive that each fasciculus is 

 composed of spiral and proper vessels, the same as 

 we have already seen constitute the ribs in the 

 leaves of monocotyledons. 



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