397); but a diagonal position of the calyx generally shows that the flower is not, strictly speaking, tetramerous, as in _Plantago_ (Fig. 567), _Veronica_ (Fig. 559 _C_) and others. If the bracteoles are _not_ typically present, then the position of the sepals is changed accordingly, and the two outer sepals endeavour to assume the position which the bracteoles would otherwise have occupied, _e.g._ in _Primula_ (Fig. 547). Other positions are also found when the number of bracteoles is more or less than two. The leaves which follow the sepals occupy definite positions with regard to them, which we may consider later. An arrangement must, however, be mentioned here; when the flower is “_diplostemonous_” that is, has two whorls of stamens (thus, Sn, Pn, An + n), these may be arranged in two ways. _Either_ the first-formed whorl of stamens, which are termed the “calyx-stamens,” stands directly in front of the sepals (that is “episepalous”), and is the _outermost_ whorl, and in this case a regular alternation takes place between sepals, petals and the two whorls of stamens, 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 Gn should be added to the formula above. _Or_, the calyx-stamens form the _innermost_ whorl, and the corolla-stamens, which are subsequently 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._ Caryophyllaceæ. 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: Apetalæ (those without corolla), Sympetalæ or Gamopetalæ (those with the petals united), and Choripetalæ or Polypetalæ (the petals not united). This division has now been abandoned because it has been proved that the Apetalæ were merely reduced or incomplete forms of the Choripetalæ, and they have therefore been distributed among the various families of the latter sub-class.