54 PRACTICAL BOTANY^ 



When opposite leaves have stipules, the latter usually oc- 

 cupy the space between the petioles on opposite sides, and 

 are then called interpetiolar stipules. The stipules of 

 each of the opposite leaves becoming thus contiguous, or 

 even continuous, each pair of leaves appears to have but a 

 single pair of stipules, as in several Madderworts. The 

 stipules of leaflets are called stipels, and leaflets with sti- 

 pels stipellate leafletSy in contradistinction to stipulate 

 leaves. 



Leaves may differ from one another in the shape of 

 their petioles. The latter, generally terete, or half-terete, 

 and not unfrequently channelled on the upper side, may 

 be winged (see § 94). Sometimes the petiole is flattened 

 at right angles with the blade, as in the Aspen ; or it is 

 dilated, helow into an inflated vnembranous sheath, as in 

 many Umbelworts. (PI. I., 37.) 



In many Endogens the leaf-like petiole consists entirely 

 of a sheath, inwrapping the stem, which in grasses bears 

 above a membranous appendage, to be regarded as a 

 double axillary stipule and called the Ugule. (PI. I., 36.) 



BB. OEGANS OF EEPEODUOTION. 

 *THE FLOWER. 



I. ESSENTIAL OEGANS' OF THE FLOWEK. 



104. The Pis^piLS vary in number. A flower with a 

 solitary pistil is said to be monogynous, and one with 

 2, 8, 4, 5, 6 or many pistils, digynous, trigynous, tet/ragy- 

 nous, pentagynous, hexagynous, pol/ygynous. When 

 in great number, they are arranged in spiral rows on 

 an enlarged receptacle, as in most Crowfoots, the Mag- 



