XVI.] 



BOTANY. 



67 



and is a part of the floral receptacle (Par. 82^). In 

 the buttercup (Fig. 22) there is no disk; in the bramble 

 (Fig. 23) it forms a thickened shining lining of the 

 base of the calyx ; in the orange (Fig. 45 a) and mig- 

 nonette (Fig. 45 ) it forms a distinct cushion; in the 



FIG. 45. Disks of, a, orange ; b, mignonette : both enlarged. 



wallflower it appears as two moist honeyed glands 

 at the base of the short stamens ; and in the carrot 

 and similar flowers it crowns the ovary. 



XVI. AESTIVATION. 



100. As the folding together of the leaves in bud is 

 called vernation (Par. 69), so that of the floral organs 

 is called aestivation. In this folding that of the sepals 

 never interferes with that of the petals, and these 

 often follow quite different plans. These plans are 

 constant throughout the flowers of any one kind of 

 plant, and the same plan prevails through many allied 

 plants ; in other words, aestivation is a guide to the 

 detection of relationships amongst plants. 



1 01. There are four principal plans of estivation. 

 T. Imbricate, when one or more pieces are outside 



