LECT. IV.] THE ROOT. BULBS. 179 



sels run vertically through each layer, communi- 

 cating with those of the caudex, the stem, and the 

 roots : these are entire and porous vessels ; but in 

 some of the laminated bulbs, the spiral vessels 

 are so numerous as apparently to make up the 

 greater part of the substance of the layers. There 

 are two species of laminated bulbs ; the concen- 

 tric and the nestling. 



1. The Concentric laminated bulb (Bulbuscon- 

 centricus tunicosus) consists of sheathing laminae, 

 each enclosing, or nearly enclosing, the other from 

 the centre to the exterior coat or tunic. This spe- 

 cies of laminated bulb may be subdivided into two 

 sections ; the first comprehending those bulbs in 

 which the layers are entire, or in which each 

 layer is the sheath, as it were, of those within it ; 

 and the second, those in which the layers are 

 divided, or only overlap those within them, but 

 do not form an entire sheath, as in the former 

 instance. 



* With entire Layers. 



The most familiar examples of this division are 

 the common Onion, Allium Cepa, and the mem- 

 bers of the Narcissus tribe. In these, the cau- 

 dex is of an irregular, serniorbicular form ; and 

 consists of a central cellular part or pith, covered 

 by a more solid envelop or cortex, which is inter- 

 posed betwixt the basis of the layers and the pith, 

 and forms also the proper radical plate, whence 



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UNIVERSITY 



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