p INTRODUCTORY. 
across a stalk of Indian Corn; these stems are called Endogenous or 
Endogens, (inside Aacigiint The terms Dicotyledonous and Exogenous 
are used synonymously, as are Monocotyledonous and Endogenous. 
20. Tue Lear. It is in the leaf that the important work of trans- 
forming the crude sap, which is taken up by the roots, into organized 
material fit = enter into the growth of the Pent, is performed. In this 
rocess the agency of sunlight is required and a free exposure to the air, 
e leaves are so made and so dispo sp the stem as to presen 
susrietBy these ———. 
2 y 
Sag and stipules may one or both be absent, the ey portion 
ing the e. Leaves bara a petiole are said to be petioled or 
tiolate ; without a petiole they are sessile. Where the b nde joins the 
petiole, or, if this be absent, the stem, is its base; the opposite ends are 
argins. 
sides gins. 
21. The blade of the leaf consists of a green pulpy substance through 
which runs a framework of fibres to give it strength ; these, as they are 
two forms: Ist, where a strong rib, (the mid ee runs from the base to 
the apex of the leaf, from which lateral veins brant off, like the plume 
upon a feather ; this is called feather-veined, or penni-nerved (Fig. 66) ; 
radiately-veined t the dems approaches the circular. The general outline 
of leaves, as well as that of pass om pores of plants, is described 
a variety of terms. A very wit. co) | margins 1s 
slag the leaves of ak pire e ees hen the blade tapers 
Wi ‘; 
up to each end, and is sever: an broad, it is /an- 
ceolate (Fig. 179) ; when broader in p portion, oblong 5 if both ends are 
ethwise, with the b: rides it is ov 
round, orbicular (Fig. 44). If the leaf taper fe base instend 
of apex, it is oblanceolate and obovate, the reverse of 
and ovate. If rounded above and long and narrow below, it is 
ate, and sik aw 
2 rounded, the 
leaf i is said to be cordate or hatha i (hie. a) 171) ; if it such a leaf be 
"much broader r than long, it vey-shaped or reniform. If the pro- 
: * 
