THE ANGIOSPERMAE 



1091 



/^^^s^OX 



Fig. 1058. — Chimonauthus fragrans. A bud and a floral diagram showing the 

 continuous sequence of bracteoles and sepals. {After Le Maoiit and 

 Decaisne.) 



the true calyx or even the entire flower bud, as in Calystegia sepimti (Fig. 

 1059), but these are exceptional occurrences and do not invalidate the 

 general conclusion of the existence of homology between the two sets of 

 organs. 



Floral symmetry is defined by the position of the flower with regard to 

 its mother-axis. The side nearest the axis is designated posterior and the 



Fig. 1059. — Calystegia sepiiim. A, The flower. B, Longitudinal 

 section, showing involucre of two bracteoles enclosing the 

 caly^x. 



side away from the axis is called anterior. The plane passing through the 

 axis from back to front of the flower is the antero-posterior or median 

 plane, that at right angles to the median is the transverse or lateral plane. 



