ANGIOSPERMS. — MONOCOTYLEDONS. 



437 



frequently of deep division, as in some Aroideae {Amorphophallm, Athentrns, 

 Saiiromatum) ; the fan-shaped and pinnate leaves of the Palms owe their division not 

 to branching at an early period of their growth, but to the tearing of their substance 

 at the time of unfolding, caused by the drying up of certain strips of tissue in the 

 lamina which is up to that time entire and is folded in sliarp plaits. 



Fig. 363. A leaf of ^A 

 /iiim Cepa divided long^itu- 

 dinally into halves ; z 

 the thickened base of the 

 sheath, whicli remains be- 

 hind as a bulb-scale after 

 the decay of the upper part 

 of the leaf, s the mem- 

 branous part of the sheath, 

 / the lamina, h the cavity 

 and ;■ the inner side of the 

 lamina, x the ligule. 



The venation of the foliage-leaves differs from that of most Dicotyledons in the 

 circumstance that the weaker veins do not usually project on the under side of the 

 leaf, but run through the mesophyll ; in smaller foliage-leaves the projecting midrib is 

 also wanting, but it is strongly developed in the large stalked leaves of the Spadici- 

 florae and Scitamineae and is traversed by numerous vascular bundles. If the leaf is 

 ribbon-shaped and with a broad insertion, the vascular bundles run nearly parallel to 

 one another ; in broader leaves without a distinct mid-rib they run in curves from the 

 central line of the leaf to the margins, as in Convallaria (Fig. 364) ; but if there is a 

 strong mid-rib in a broad lamina, as in Musa, etc., the vascular bundles of the mid- 

 rib give off slender lateral bundles which run in large numbers parallel to one another 

 to the margin of the leaf; these parallel veins crossing the loaf are sometimes 



