GROUP V. AXGIOSPERM.E. 449 



peculiarities of form are overlooked. Thus the diagram Fig. 264 

 may be expressed by the formula KB, C\ A3 + 3, (?, which 

 means that the calyx jfiT, and the corolla C, each consist of a single 

 whorl of three members, the androecium of two whorls each of 

 three members, and the gynaeceum of one whorl of three members, 

 all in regular alternation. When one whorl is superposed on 

 another, the superposition is indicated in the formula by a line | 

 between the whorls. If the number of members in any whorl is 

 variable, the letter n is used instead of a number. Thus, for 

 instance, Kn, C*n, An + n, Go. is the theoretical formula' of most 

 Monocotyledons. The absence of a whorl is expressed by a cypher 

 0, and of individual members by the number of those actually 

 present. Thus the formula for the flower of a Grass (Fig. 2G5) is 

 AT), (70, A3 + 0, G l . Superior and inferior ovaries are indicated 

 by a stroke below or above the corresponding figure, and duplica- 

 tion by the exponent 2 ; thus the diagram Fig. 266 is represented 

 by the formula K2 + 2, C x 4, A2 + 2 2 , G, the x after C in- 

 dicating that the position of the petals is diagonal, i.e. that the 

 four petals alternate with the four sepals, as if the latter all 

 belonged to the same whorl. The bracket in which the number of 

 the carpels of the gynseceum G is enclosed, indicates that the 

 members thus bracketed are coherent. Staminodia may be dis- 

 tinguished by a -j- before the figure. When the perianth is not 

 differentiated into calyx and corolla, it is expressed by the letter 

 P: thus the formula for the flower of Chenopodium is P5 | A5 



<T. 



The Number of Members in a Whorl shows considerable varia- 

 tion : thus, in Monocotyledons it is generally three (rarely two or 

 five), whereas in Dicotyledons it is frequently five, less frequently 

 two or four, rarely three (e.g. Berberis, Rheum, Polygonum). The 

 number of members in a whorl is indicated by the terms di- tri- 

 tctra- penta-merous, etc. Whorls containing the same number 

 of members are said to be isomerous ; or, when the number of 

 members is not uniform, heteronierous. Flowers having isomerous 

 whorls are said to be encyclic or isocyclic, whereas when the 

 whorls are heteronierous the flowers are said to be heterocyclic. 

 Of these two conditions the latter is the more common, though the 

 former is frequently realized (e.g. many Monocotyledons). The 

 heterocyclic condition is due either to the number of members in 

 one or more of the whorls being smaller (oligomery) or greater 

 (pleiomery} than that which is the typical number. The com- 



