66 TEXTURE OF VEGETABLES. 



the form of a hollow cylinder, by the side of the nak- 

 ed stem, and both portions retaining their original con- 

 nexion with the trunk and superior branches. After 

 a few years this tree was examined, and "the cylinder 

 of bark was found lined with layers of new wood, whose 

 numbers added to those of the wood from which it had 

 been stripped, made up the number of rings in the 

 branch above and below the experiment." But the 

 stem from which the bark had been removed remained 

 unaugmented. It appears therefore that two layers are 

 annually deposited on the inner surface of the bark, 

 similar at first and closely united, but gradually assu- 

 ming a distinct character, and at last receding from 

 each other in the form of wood and bark. At the com= 

 mencement of a second Spring, they are contiguous 

 but readily detached from each other, but ever after 

 wards are they separated by the intervention of the 

 more recent layers. 



SECTION 5 



PITH. 



The pith is a soft spongy substance occupying the 

 entre of the stem, and extending from the root to the 

 extremity of the young branches. In the Ash it is un- 

 interrupted and compact, in the Garget Phytolacca de~ 

 candra, it is composed of transverse partitions inter- 

 secting the tube of the stem, which in that plant is un- 

 usually large ; and in some of the Thistles, it more re- 

 sembles the web of a spider attached to the sides of the 

 tube, but neither regularly disposed nor so large as to 

 occupy its entire cavity. In the Hemlock and other 



