100 STRUCTURAL BOTANY. [85. 



here also preceded by a rootlet. Some plants are thus 

 artificially propagated in conservatories from the influ- 

 ence of heat and moisture on a leaf or the fragment 

 of a leaf, as Begonia. 



252. Vernation or praefoliation are terms denoting 

 the mode of arrangement and folding of the leaf 

 organs composing the bud. This arrangement is defi- 

 nitely varied in different orders of plants, furnishing 

 useful distinctions in systematic botany. It may be 

 studied to excellent advantage by making with a keen 

 instrument a cross-section of the bud in its swollen 

 state, just before expansion ; or it may be well ob- 

 served by removing one by one the scales. The Forms 

 of Vernation are entirely analogous to those of ^Esti- 

 vation, and denoted by similar terms. 



253. Vernation is considered in two different as- 

 pects first, the manner in which the leaf itself is 

 folded ; second, the arrangement of the leaves in re- 

 spect to each other. This depends much upon the 

 Phyllotaxy. ( 261.) 



288 



Vernation, 277, of Oak leaf ; 278, of Liriodendron (Tulip-tree). 279, of Fern ; 280, of Carex ; 281, Sage ; 



282, Iris. 



254. Each leaf considered alone is either flat and 

 open, as in the Mistletoe, or it is folded or rolled, as 

 follows : viz., Reclined, when folded crosswise, with 

 apex bent over forward toward the base, as in the 

 Tulip-tree ; Conduplicate, when folded perpendicularly, 



