336 DICOTYLEDONES. 



which is also continued into the carpels if their number is the 

 same as that of the other whorls : the carpels are then placed 

 opposite the sepals (Fig. 278) and the flower is isomerous and Grn 

 should be added to the formula above. Or, the calyx-stamens 

 form the innermost whorl, and the corolla-stamens, which are sub- 

 sequently formed (" epipetalous " stamens), stand outside these 

 (Figs. 360, 429) ; if the number of carpels is the same as that of 

 the preceding whorls, they are often placed right in front of the 

 petals and the corolla-stamens. The first-mentioned arrangement 

 is termed Diplostemonous, and the second Obdiplostemonous. Both 

 arrangements may be found in one and the same order, e.g. Caryophyllacese. 

 The size and relation of the members of the flowers, and also the contact with 

 other members in the early stages of their development, play an important 

 part in determining the arrangement. 



The great number of structural arrangements found in this 

 enormously large class, may, as is the case in the Monocotyledons, 

 be further varied by suppression and division of certain leaves 

 (especially the stamens). Instances of this will occur in the 

 following (Figs. 559, 568. 426, 441, 445, etc.). 



The Dicotyledons were formerly divided into 3 sub-classes : 

 Apetala? (those without corolla), Sympetalaa or Gamopetala? (those 

 with the petals united), and Choripetalaa or Polypetalae (the petals 

 not united). This division has now been abandoned because it has 

 been proved that the Apetalas were merely reduced or incomplete 

 forms of the Choripetalse, and they have therefore been distributed 

 among the various families of the latter sub-class. 



With regard to the Sym petals (or Gramopetalae) it may be 

 stated that they form to a very great extent a closely connected and 

 natural group, having in common not only the character that the 

 corolla is gamopetalous and the stamens united with it (this being 

 also found in the Cboripetalas), but also a great many others (such 

 as persistent calyx, cyclic flowers with the formula S5, P5, A5 and 

 as a rule Gr2, the two carpels being united to form the ovary ; seeds 

 Avith a thick integument and a very small nucellus). They are 

 therefore considered as an independent sub-class, and must be 

 placed at the close of the system of classification as the forms 

 which presumably have arisen the latest. In the future systems 

 of classification this arrangement will very probably be changed, 

 and the first families of the Sympetalee, the Bicornes and others 

 will for instance be to a certain extent united with the families or 

 orders of the Choripetalse. The Sympetala? may certainly be con- 



