THE LEAVES OF VASCULAR PLANTS. 297 



folded petiole ; thus, the petioles of the Potaraogetons 

 approach in this respect those of the Iris ; the leaves of 

 several Hyacinths are nearly folded lengthways, &c. 



A third disposition, entirely peculiar to Monocotyle- 

 dons provided with limbs, is that of being Convolute ; 

 that is to say, of having the limb rolled in the form of 

 a cone upon one of its edges which proceeds from the 

 axis ; it is this which is found in the Scitamineae and 

 Amomeas. 



Almost all the leaves of plants enter into one of the 

 dispositions which I have mentioned ; but there are some 

 which seem formed upon an entirely different type, and 

 instead of being folded in a longitudinal direction, are 

 so in a transverse one. Such are — 



1st. Leaves said to be Replicate ; that is to say, 

 those which are folded so that their upper part is applied 

 to the lower ; this is observed in the leaves of Aconitum, 

 The young leaves of the Tulip-tree ( Liriodeniron tulipi- 

 fera) have the petiole curved, so that the limb is folded 

 back upon the base, and may be considered as belonging 

 to this class. 



2d. CiRCiNNATE Leaves : that is to say, those which 

 are rolled up from the apex to the base, the point of the 

 leaf, or of each of its lobes, serving as the axis of the 

 roll. This takes place in Dicotyledons in the Droseraceae, 

 in Monocotyledons in the Cycadeae, and is found in the 

 highest degree in the Ferns. 



As soon as leaves begin to grow, they are seen to 

 elongate and enlarge very regularly ; but the laws of 

 this growth are not as well known as could be desired. 



Petioles formed of parallel fibres, and of a foliaceous 

 appearance, as those of Monocotyledons, and particu- 

 larly the foliaceous organs, which, for the sake of abbre- 

 viation, are called leaves in Hyacinths and other bulbous 

 plants, elongate in a manner peculiar to them — viz. 



