ANATOMY OP LEAVES. 



567 



LECT. X.] 



the margin they all inosculate, and form, as it 

 were, one fasciculus which, extending from the base 

 to the apex, is the real living boundary of the leaf. 

 Pursuing our examination more closely ; and 

 placing a slice (23.) of the petiole cut transversely 

 near the base of the expansion, under the micro- 

 scope with a glass of a moderate power, we per- 

 ceive that the vessels are arranged in distinct fas- 

 ciculi, which are nearly of the same size in the cen- 

 tre of the section ; alternately larger and smaller 

 (23. a. b. a. b.) near the circumference on the con- 

 vex surface, or that part of the petiole which is 

 towards the under disk of the leaf; and all small 





(c. c. c. c. c. c.) on the concave surface. The costae 

 (22. e. e. e.) are continuations of those on the con- 

 owing to the dark green colour of the parenchyma in the meshes 

 formed by these threads. 



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