508 



BOTANY 



PART n 



li vision r,in only be made by two such planes of section the flower is BISYMMETKICAL 

 or BILATERAL (c.<j. />t\'iitt,'(i, belonging to the Fumariaceae). From the originally 

 radial type the PORSIVEXTUAL (SYMMETRICAL, ZY<;OMORPHIC), and the A^YM- 

 MF.Tiii' A i. type> .-an 1- derived by the unequal si/e of ^nme of tlie inembers or 

 tlieir displacement or suppression (Fig. 484 H, C ; cf. p. 16). In zygomorphic 

 flowers there is only one plane of symmetry by which the flower can be divided 

 into corresponding halves ; while in asymmetrical flowers no such plane of symmetry 

 exists. Dorsiventral flowers tend to take up a particular position in relation to 

 the directive force of gravity and exhibit a high degree of adaptation to insect 

 pollination. According to whether the plane of symmetry coincides with the 



MEDIAN PLANE of the 



flower (i.e. the plane 

 passing through the axis 

 of the flower and the main 

 axis), forms an acute 

 angle with the median 

 plane, or is at right 

 angles to it, flowers are 

 distinguished as MED- 



IANLY DORSIVEXTRAL, 

 OBLIQUELY DORSIVEX- 

 TRAL, Or TRANSVERSELY 

 IMIRSIVEXTRAL res) - 



tively (Fig. 485). Radi- 



Fl<!. 485. Flowers of, A, SiiitiUm-in nl/iiiia, iiiiMlianly xyj, r n- 

 morphic(ilorsivi-ntral) ; /;, .If'gtxilvjhiiipocattainivi, obliquely 

 xynoinorpliie (tlorsiventral) ; '', I'oryilalis Intea, tiiinsvi-isi-ly 

 y.yX'iinorpli if (dorsi ventral) ; il, hrart-. 



Fn.. -!'>. Diagram of a penta- 

 cyclic flower (Lilium). 



ally symmetrical monstrosities of normally zygomorphic flowers are termed 



I'ELORIC. 



If a diagram of the arrangement of the members as they are seen in a crn-s 

 section of an opened flower-bud is constructed (p. 16) and so oriented that the 

 transverse section of the axis of the inflorescence stands above, that of the bract 

 In-low the ground plan of the flower, what is known as a FLORAL DIAGRAM is obtained. 

 The accompanying floral diagram (Fig. 486) is that of a monocotyledonoiis flower 

 with live whorls of members. A FLORAL FORMULA gives a short expression for the 

 members of a flower as shown in the floral diagram. Denoting the calyx by K, 

 the corolla by C (if the perianth forms a. perigone it is denoted by P), the androe- 

 cium by A, and the gynaeceum by G, the number of members in each case is 

 placed after the letter. Thus the floral formula of the monocotyledonoiis flower 

 represented in Fig. 486 would be, P3 + 3, A 3 + 3, G 3. When tin-re is a large 



