240 



THE FLOWER. 



cgp 



ing organs, are generally multiplied in each flower, so as greatly to 

 diminish the chances of failure. Thus we find a circle or whorl 

 of each kind of organ, and often two or three circles, or a still lar- 

 ger and apparently indefinite number of parts. In fact, the floral 

 organs usually occur in twos, threes, fours, or fives, and the same 

 number commonly prevails through the several parts of the flower 

 (except when interfered with by some of the disturbing causes 



hereafter mentioned), 

 which therefore dis- 

 plays a symmetrical 

 arrangement, or a man- 

 ifest tendency towards 

 it.* 



439. Having already 

 noticed the symmetri- 

 cal arrangement of the foliage 

 (234-252), and remarked the transition of ordi- 

 nary leaves into those of the blossom (426), we 

 naturally seek to bring the two under the same 

 general laws, and look upon each floral whorl as 

 answering either to a cycle of alternate leaves 

 with their respective internodes undeveloped 

 (237 - 239 ) , or to a pair or verticil of opposite or 

 verticillate leaves (250, 251). Thus, the simplest 

 combination, where the organs are dimerous, or 

 in twos, may be compared with the alternate two- 

 ranked arrangement (237), the calyx, the corolla, 

 stamens, &c., each consisting of one cycle of two 

 elements ; or else with the case of opposite leaves (250), when 



* Terms expressive of the number of parts which compose each whorl or 

 kind of organ are formed of the Greek numerals combined with pepos, a part. 

 Thus a flower with only one organ of each kind, as in the diagram, Fig. 276, 

 is monomerous ; a flower or a whorl of two organs is dimerous (Fig. 298) ; of 

 three (as in Fig. 277), trimerous; of four, tetramerous (Fig. 280) ; of five (as in 

 Fig. 284), pentamerous ; of six, hexamerous; often, decamerous, &c. 



FIG. 277. Parts of a symmetrical trimerous flower (Tillsea muscosa) : a, calyx; b, corolla; 



c, stamens ; d, pistils. 



FIG. 278. Ideal plan of a plant, with the simple stem terminated by a symmetrical penta- 

 merous flower ; the different sets of organs separated to some distance from each other, to show 

 the relative situation of the parts ; one of each, namely, a, a sepal, b, a petal, c, a stamen, and 



d, a pistil, also shown, enlarged. 



