206 OUTLINES OF PLANT LIFE. 



293. Calyx and corolla. — The leaves of the perianth are 

 usually arranged upon the torus in two or more circles or in 

 a low spiral. They may be all alike or differentiated into 

 two series, an outer and an inner. In the latter case those 

 of the outer row or rows constitute the calyx, and the inner 

 set the corolla. 



The calyx leaves, or sepals, are generally green and show a 

 great variety of form. When separate, the sepals are usually 

 sessile and broad, with more or less pointed apex. The 

 sepals are often apparently united, the originally separate 

 portions appearing as teeth or lobes at the rim of a cup or 

 tube, or some similar structure. Occasionally the sepals are 

 not persistent, but fall as the bud opens or shortly thereafter. 

 More commonly, however, the calyx, especially when un- 

 divided, remains throughout the entire development of the 

 flower, and often of the fruit. 



The inner set of perianth leaves, the petals, constitutes the 

 corolla. The corolla presents a greater variety of form and 

 color than does the calyx. 



The corolla is ordinarily not persistent, usually falling or 

 withering shortly after the microspores have been lodged 

 upon the stigma. 



294, Irregularity. — The parts of both corolla and calyx 

 are often of equal size and like shape, and may be divided 

 into several like halves by radial planes (figs. i68, 169). 

 But often the symmetry of the calyx, and still more fre- 

 quently that of the corolla, is so altered by unequal growth 

 of the parts that the flower can be divided into like halves by 

 only one, or at most two, planes; or it may even be entirely 

 unsymmetrical. This unlikeness in the size and shape of the 

 accessory leaves not infrequently extends to the stamens and 

 pistils (figs. 170, 171). 



The irregular form and color of the perianth (when other 

 than green), including the variegation of the ground color 



