112 



STRUCTURAL BOTANY. 



335. ^Estivation of the flower-bud. This terra (from 

 cestivus, of Summer) refers to the arrangement of the floral 

 envelopes while yet in the bud. It is an important subject, since 

 in general the same mode of aestivation regularly characterizes 

 whole tribes or orders. It is to the flower-bud what vernation 

 (uvrnus, Spring) is to the leaf-bud. The various modes of aesti- 

 vation are best observed in sections of the bud made by cutting 

 it through horizontally when just ready to open. From such 

 pections our diagrams are copied. 



t!5. Ranunculus acris; a single flower. 416, R. acris. P. plena, a double flower. 417, Epacris impress* 

 the flowers changing to leafy branches (Lindley). 



336. Separately considered, we find each organ here folded 

 in ways similar to those of the leaf-bud ; that is, the sepal 01 

 the petal may be convolute, involute, revolute, etc., terms already 

 defined. Collectively considered, the estivation of the flower 

 occurs in four general modes with their variations the valvate, 

 the contorted, imbricate, and plicate. 



337. In valvate aestivation the pieces meet by their mar- 

 gins without any overlapping ; as in the sepals of the Mallow, 

 petals of Hydrangea, valves of a capsule. The following va- 



