ESTIVATION OR PREFLORATION. 269 



retarded, so that the stamens are earlier completed, and their 

 antliers surpass them, or often finish their growth, while the petals 

 are still minute scales : at length they make a rapid growth, and 

 enclose -the organs that belong above or within them. Unlike the 

 sepals in this respect, the base of the petal is frequently narrowed 

 into a portion which corresponds, more or less evidently, to the 

 petiole (the clmo), and which, like the petiole, does not appear until 

 some time after the blade or expanded part ; the summit being al- 

 ways the earliest and the base the latest portion formed. As the 

 en^■elopes of the flower grow and expand, those of each circle adapt 

 themselves to each other in various ways, and acquire the relative 

 positions which they occupy in the floAver-bud. Their arrangement 

 in this state is termed 



491. Their iEstivatioii or Prirfloration. The latter would be the 



preferable term ; but the former is in common use ; the word ^sti- 

 vation (literally the summer state) having been devised for the 

 purpose by Linnisus ; — for no obvious reason except that he had 

 already apphed the name of Vernation (the spring state) to express 

 the analogous manner in which leaves are disjiosed in the leaf-bud. 

 The same terms are employed, and in nearly the same way, in the 

 two cases, but with some peculiarities. As to the dic'^rc'^'cn of 

 each leaf taken by itself, the corresponding terms of vernation (257) 

 wholly apply to ajstivation The arrangement in the bud of the 

 several members of the same floral circle in respect to each other, is 

 of much importance in systematic botany, on account of the nearly 

 constant characters that it furnishes, and also in structural botany, 

 from the aid it often affords in determining the true relative super- 

 position or succession of parts on the axis of the flower, by observ- 

 ing the order in which they overlie or envelope each other. 



492. The various forms of aestivation that have been distinguished 

 by botanists may be reduced to three essential kinds, namely, the 

 imbricative, the contorted or convolutive, and the valvular* 



493. Imhricative aestivation, in a general sense, comprises all 

 the modes of disposition in which some members of a floral circle 

 are exterior to the others, and therefore overlie or enclose them in 



* Wc should properly say of the oestivation that it is imbricative, convolutive, 

 valvular, &c., and of the calyx and corolla, or of the sepals, &c., that they are 

 imbricate or imbricated, convolute, valvate, &c. ia aestivation; but such precision 

 of language is seldom attended to. 



90* 



