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 stijpnles. 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 stijpels^ and leaflets with sti- 

 pels stipellate leaflets, in contradistinction to stimulate 

 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 § 91). Sometimes the petiole is flattened 

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

 dilated heloio into an inflated memhranoiis 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 lignle. (PI. I., 36.) 



BB. OEGANS OF EEPEODUCTION. 

 *THE FLOWER. 



I. ESSEIsTIAL ORGANS OF THE FLOW^EK. 



104, The Pistils vary in number. A flower with a 

 solitary pistil is said to be ononogynous, and one with 

 2, 3, 4, 5, 6 or many pistils, digynous, trigynous, tetragy- 

 nmis, pentoygynous, hexagynous, poly gy nous. Wlien 

 in great number, they are aiTanged in spiral rows on 

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



