CHAPTER XVI. THE SPERMAPHYTA. 



383 



quently stipulate, often toothed, incised, or branched into 

 compound forms ; with very few exceptions, their venation is 

 reticulate, and the veins, except in succulent forms, are promi- 

 nent on the lower surface. They are most commonly petiolate, 

 seldom sheathing or clasping, and, in most instances, are articu- 

 lated to the stem. 



The flowers present very great diversity both of form and 

 arrangement. In the majority of cases the floral organs consist 

 of four alternate whorls, one of sepals, one of petals, one of 

 stamens and one of pistils. See Fig. 577, A. The prevailing 



Fig. 577. — Floral diagrams of flowers of Dicotyledons. A, diagram of flower of Aralia, 

 consisting of four whorls of five alternating parts each: B, diagram of flower of Composite, 

 calyx wanting (or only represented in the pappus), the pistil consisting of two coalesced 

 carpels and five each of the petals and stamens ; C, diagram of tetramerous flower of Olea- 

 ceae, two stamens and two carpels wanting. 



numerical plan is that of five, Dut not uncommonly the parts are 

 in fours (see Fig. 577, C), less frequently they are in twos, threes 

 or sixes. There are, however, numerous deviations from the 

 type, due either to the suppression of some of the whorls or a 

 part of them, or to the abnormal multiplication of some of them. 

 The corolla, particularly, is liable to be wanting, and the sta- 

 mens are especially liable to consist of multiple whorls. In the 

 Magnoliaceae, the Ranuculaceae, the leafy Calycanthaceae and the 

 Nympheaceae, some or all of the floral organs may be arranged 

 in spirals rather than whorls. 



When both whorls of the perianth are present, they are sel- 

 dom alike, but are differentiated into calyx and corolla. Irregu- 

 lar and asymmetrical flowers are more common in Dicotyledons 

 than in Monocotyledons, the stamens, like the ordinary leaves 



