DICOTYLEDONES. 335 



whorls of stamens) are most frequently 4 or 5 in number and 

 placed in regular alternation, whilst the innermost one (the car- 

 pels) has generally fewer members, probably on account of 

 space (Figs. 360, 361, 421, 429, 487, etc.). Trimerous (Figs. 384, 

 387, etc.) flowers, or those in which the members of the flower are 

 in threes or a multiple of three, also occur, as well as dimerous 

 flowers ; other numbers are rare. It is of the greatest importance 

 in connection with the relative position of the members of the 

 flower to the axis and bract (orientation), whether the bracteoles 

 are typically present (even, thougfh they may not be developed), or 

 are typically absent. If there are 2 bracteoles present, then their 

 position in a pentamerous flower is often as follows: the first sepal 

 turns obliquely forward, the second is posterior and median, the 

 third obliquely forward, the fourth and fifth obliquely backward ; 

 quincnncial aestivation is often found in these buds (Figs. 360, 429, 

 471, 475, 584). The first and third leaves, in the following chapters, 

 are most frequently alluded to as the " anterior," the fourth and 

 fifth as the " lateral " leaves. The reversed arrangement, with the 

 median sepal in the front, occurs for instance in Papilionacece 

 (Fig. 511), Lobeliacece (Fig. 594), Rhodoracece. If any bracteoles are 

 present below a tetramerous flower, the relation is generally that 

 2 sepals (the first ones) stand in the median plane, the two next 

 ones transversely (Fig. 393), and the corolla then adopts a diagonal 

 position (Fig. 397) ; but a diagonal position of the calyx generally 

 shows that the flower is not, strictly speaking, tetramerous, as in 

 Plant ago (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 en- 

 deavour 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 arrange- 

 ment must, however, be mentioned here ; when the flower is 

 " diplostemonous," that is, has two whorls of stamens (thus, Su, 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, 



