THE CALYX AND COROLLA 115 



in the order Composite. In the large majority of plants the 

 calyx is developed first, then the corolla, and then the 

 stamens. 



e. Within the whorl of stamens there arises, at the margin 

 of the now much depressed apex, the last series of floral 

 organs, viz. two carpels, which arch over the apical depression, 

 and thus close in the cavity of the inferior ovary. 



f. All the organs increase in size, while from the base of the 

 cavity of the ovary a papilla arises, which develops into a 

 single anatropous ovule, with one integument, and small 

 nucellus. 



II. Cut horizontal (i.e. transverse) sections of a capitulum : 

 treat as before : examine with a low power. 



Note the arrangement of bracteoles, with young flowers in 

 their axils, round the central naked apex. The youngest 

 flowers will appear simply circular in outline (simple papillae of 

 stages a and b) ; older flowers will show successively 



i. The five papillae of the corolla (petals) uniting at an early 

 stage into the gamopetalous corolla-tube. (Stage <r.) 



ii. Five stamens, alternating with the petals. (Stage d.) 



iii. Centrally two carpels. (Stage e.} 



Other Composites may be taken as substitutes for Helianthus, 

 but some variety will be found in different genera in the 

 character of the bracteoles, and in the calyx : thus in 

 Chrysanthemum Leucanthemum, which is a useful type, the 

 bracteoles are absent, and there is no representative of the 

 calyx. 



CALYX AND COROLLA. 



Mount in glycerine two small pieces of the corolla of a ligulate 

 floret of the Sunflower which has been kept in spirit, the one 

 with the lower, the other with the upper surface uppermost. 

 Examine under a low power and note, the delicate texture and 

 transparency of the whole : the rarity or even entire absence 

 of stomata : the numerous hairs on the lower, and the small 

 projecting papillae on the upper surface : and the vascular 

 bundles which do not form a dense network as in the foliage 

 leaf. 



I 2 



